JP5871715B2 - Frequency divider and semiconductor device using the frequency divider - Google Patents

Description

The present invention relates to a frequency divider circuit. Further, the present invention relates to a semiconductor device using a frequency dividing circuit.

Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and a semiconductor element, an electro-optical device, a memory device, a signal processing device, a semiconductor circuit, and an electronic device are all semiconductor devices. It is.

Semiconductor devices such as a central processing unit (CPU) have various configurations depending on the application. Such a semiconductor device includes a plurality of circuits. For example, in addition to a circuit (main memory) for storing data and programs, various storage circuits such as a register and a cache memory are provided. ing.

The register has a role of temporarily holding a data signal for arithmetic processing by an arithmetic circuit, holding of an execution state of a program, and the like. The cache memory is provided between the arithmetic circuit and the main memory for the purpose of reducing the access to the low-speed main memory and speeding up the arithmetic processing by the arithmetic circuit.

In such a semiconductor device having a plurality of circuits, a high-frequency clock signal generated by an oscillation circuit is converted into a low-frequency clock signal using a frequency divider, and the converted clock signal is synchronized with each circuit. Used to take.

The frequency dividing circuit is generally configured using a delay flip-flop (DFF) circuit (see, for example, Patent Document 1).

JP 2000-2224026 A

First, an example of the configuration and operation of a general frequency divider will be described with reference to FIG. FIG. 9A is a block diagram of a frequency dividing circuit 100 using a DFF (Delay Flip Flop) circuit. The frequency dividing circuit 100 has a configuration in which three DFF circuits indicated by a DFF circuit 101, a DFF circuit 102, and a DFF circuit 103 are connected in series in three stages.

The DFF circuit 101 to DFF circuit 103 each have a clock signal input unit CK, an input unit D, an output unit Q, and an output unit Q bar. In the DFF circuit 101, the clock signal input unit CK is electrically connected to the terminal unit 111. A clock signal CLK having a specific frequency is input to the terminal unit 111. The clock signal CLK input to the terminal unit 111 is input to the DFF circuit 101 via the clock signal input unit CK. The output part Q bar of the DFF circuit 101 is electrically connected to the input part D of the DFF circuit 101. The output unit Q of the DFF circuit 101 is electrically connected to the clock signal input unit CK of the DFF circuit 102 via the node 112. The output part Q bar of the DFF circuit 102 is electrically connected to the input part D of the DFF circuit 102. The output unit Q of the DFF circuit 102 is electrically connected to the clock signal input unit CK of the DFF circuit 103 via the node 113. The output part Q bar of the DFF circuit 103 is electrically connected to the input part D of the DFF circuit 103. The output unit Q of the DFF circuit 103 is electrically connected to the terminal unit 114.

FIG. 9B is a diagram showing a configuration of a general DFF circuit 101 using circuit symbols. A DFF circuit 101 illustrated in FIG. 9B includes an inverter 121, an inverter 122, and an inverter 123, an analog switch 124 and an analog switch 125, a clocked inverter 126, and a clocked inverter 127.

In FIG. 9B, a node 115 to which the terminal portion 111 and the input portion of the inverter 121 are connected corresponds to the clock signal input portion CK. Inverter 121 generates clock bar signal CLKB, which is an inverted signal of input clock signal CLK, and outputs it to node 116. The analog switch 124, the analog switch 125, the clocked inverter 126, and the clocked inverter 127 operate in synchronization with the clock signal CLK and the clock bar signal CLKB. The input of the analog switch 124 corresponds to the input unit D, and the output of the analog switch 125 corresponds to the output unit Q bar.

Note that the DFF circuit 102 and the DFF circuit 103 also have the same configuration as the DFF circuit 101.

FIG. 9C is a timing chart for explaining the operation of the frequency divider circuit 100 and shows changes in potential of the terminal portion 111, the node 112, the node 113, and the terminal portion 114 with time. The clock signal CLK input to the terminal unit 111 is output to the node 112 after the frequency is halved (the cycle is doubled) by the DFF circuit 101.

In addition, the clock signal CLK input to the terminal portion 111 is output to the node 113 by the DFF circuit 101 and the DFF circuit 102 having a frequency that is ¼ times (period is four times).

The clock signal CLK input to the terminal portion 111 is output to the terminal portion 114 after the frequency is 1/8 times (the cycle is 8 times) by the DFF circuit 101, the DFF circuit 102, and the DFF circuit 103. . Thus, every time the DFF circuit is increased by one stage, the frequency of the clock signal CLK is halved.

Next, FIG. 10 is a circuit diagram illustrating the circuit symbol illustrated in FIG. 9B and its circuit configuration.

10A1 is a circuit symbol indicating an inverter, and FIG. 10A2 is a circuit diagram illustrating a circuit configuration of the inverter. The inverter includes a p-type transistor 131 and an n-type transistor 132, and one of the source and drain of the p-type transistor 131 is electrically connected to the high power supply potential VDD, and the other of the source and drain is electrically connected to the output terminal Out. Connected. One of the source and the drain of the n-type transistor 132 is electrically connected to the low power supply potential VSS, and the other of the source and the drain is electrically connected to the output terminal Out. The gates of the p-type transistor 131 and the n-type transistor 132 are electrically connected to the input terminal In.

Here, the high power supply potential VDD (hereinafter also simply referred to as “VDD”) indicates a power supply potential higher than the low power supply potential VSS. The low power supply potential VSS (hereinafter, also simply referred to as “VSS”) indicates a power supply potential lower than the high power supply potential VDD. Alternatively, the ground potential can be used as VDD or VSS. For example, when VDD is a ground potential, VSS is a potential lower than the ground potential, and when VSS is a ground potential, VDD is a potential higher than the ground potential.

The inverter has a function of inverting an input signal and outputting the inverted signal. For example, when a signal corresponding to “1” (for example, VDD) is input to the input terminal In of the inverter, “0” (for example, VSS) is output to the output terminal Out. When a signal corresponding to “0” is input to the input terminal In of the inverter, “1” is output to the output terminal Out.

FIG. 10B1 is a circuit symbol showing an analog switch, and FIG. 10B2 is a circuit diagram illustrating a circuit configuration of the analog switch. The analog switch includes an n-type transistor 133 and a p-type transistor 134. One of the source and drain of the n-type transistor 133 and one of the source and drain of the p-type transistor 134 are electrically connected to the input terminal In. The other of the source and the drain of the n-type transistor 133 and the other of the source and the drain of the p-type transistor 134 are electrically connected to the output terminal Out. In this example, the clock signal CLK is supplied to the gate of the p-type transistor 134 and the clock bar signal CLKB is supplied to the gate of the n-type transistor 133.

With such a configuration, the input terminal In and the output terminal Out can be made conductive and non-conductive in synchronization with the clock signal CLK and the clock bar signal CLKB.

FIG. 10C1 is a circuit symbol illustrating a clocked inverter, and FIG. 10C2 is a circuit diagram illustrating a circuit configuration of the clocked inverter. In the clocked inverter, a p-type transistor 135 is further provided between the p-type transistor 131 and VDD of the inverter shown in FIG. 10A2, and an n-type transistor 136 is further provided between the n-type transistor 132 and VSS of the inverter. It has the structure which provided.

Specifically, one of the source and the drain of the p-type transistor 135 is electrically connected to VDD, and the other of the source and the drain is electrically connected to one of the source and the drain of the p-type transistor 131. One of the source and the drain of the n-type transistor 136 is electrically connected to VSS, and the other of the source and the drain is electrically connected to one of the source and the drain of the n-type transistor 132. FIG. 10C2 illustrates an example in which the clock bar signal CLKB is supplied to the gate of the p-type transistor 135 and the clock signal CLK is supplied to the gate of the n-type transistor 136.

When the p-type transistor 135 and the n-type transistor 136 are on, the clocked inverter receives “0” (to the output terminal Out when a signal corresponding to “1” (for example, VDD) is input to the input terminal In. For example, VSS) is output. When a signal corresponding to “0” (for example, VSS) is input to the input terminal In when the p-type transistor 135 and the n-type transistor 136 are on, “1” (for example, VDD) ) Is output. Further, no output is made when the p-type transistor 135 and the n-type transistor 136 are off.

With such a configuration, the input signal can be inverted and output in synchronization with the clock signal CLK and the clock bar signal CLKB.

As described above, in the conventional frequency dividing circuit 100, three inverters, two analog switches, and two clocked inverters are used in one DFF circuit 101, and at least a total of 18 transistors are used. As a result, there is a problem that the occupied area becomes large. In addition, since the number of transistors used is large, there is a problem that power consumption increases.

Further, in the conventional inverter, when the output signal is switched from “1” to “0”, or from “0” to “1”, a through current is easily generated between VDD and VSS, and it is difficult to reduce power consumption. There was a problem.

By configuring the frequency divider circuit with a smaller number of transistors than in the past, the area occupied by the frequency divider circuit and power consumption can be reduced.

One embodiment of the present invention includes a first inverter and a second inverter, first and fifth transistors that are p-type transistors, and second to fourth transistors that are n-type transistors; And one of a source and a drain of the first transistor and the fifth transistor is electrically connected to the first power source, and the source or the drain of the first transistor Is electrically connected to one of the source and the drain of the second transistor, the other of the source and the drain of the second transistor is electrically connected to one of the source and the drain of the third transistor, The other of the source and the drain of the fifth transistor is electrically connected to one of the source and the drain of the sixth transistor. The other of the source and the drain of the sixth transistor is electrically connected to one of the source and the drain of the seventh transistor, and the other of the source and the drain of the third transistor and the source or the drain of the seventh transistor. Is electrically connected to the second power source, and the gate of the first transistor and the gate of the second transistor are electrically connected to the gate of the eighth transistor and the input of the first inverter. One of the source and the drain of the eighth transistor is electrically connected to the other of the source and the drain of the first transistor and one of the source and the drain of the second transistor, and the source or the drain of the eighth transistor The other of the drains is electrically connected to the gate of the seventh transistor, and the input of the second inverter And the other of the source and drain of the fifth transistor and one of the source and drain of the sixth transistor are electrically connected, and the output of the second inverter is electrically connected to one of the source and drain of the fourth transistor. The other of the source and the drain of the fourth transistor is electrically connected to the gate of the third transistor, and the output of the first inverter is connected to the gate of the fourth transistor, the fifth and the fifth 6 is electrically connected to the gate of the transistor No. 6;

The first power supply supplies a higher potential than the second power supply. In addition, the off-state current of a transistor including an oxide semiconductor in a semiconductor layer in which a channel is formed (hereinafter also referred to as an OS (Oxide Semiconductor) transistor) is significantly smaller than that of a transistor using silicon.

By using an OS transistor as the fourth transistor, the potential of a node connected to the source or drain of the fourth transistor can be stably maintained. In addition, by using an OS transistor as the eighth transistor, the potential of the node connected to the source or the drain of the eighth transistor can be stably maintained.

The OS transistor can also be used as a transistor other than the fourth transistor or the eighth transistor. In this manner, by using an OS transistor, a semiconductor device with stable operation and high reliability can be realized.

According to one embodiment of the present invention, a divider circuit with a small occupation area can be provided.

According to one embodiment of the present invention, a frequency divider circuit with reduced power consumption can be provided.

By using the divider circuit which is one embodiment of the present invention, a semiconductor device with reduced power consumption can be provided.

According to one embodiment of the present invention, a highly reliable semiconductor device with stable operation can be provided.

One embodiment of the present invention solves at least one of the above problems.

The figure which shows the structure of a frequency divider circuit and FF circuit. The figure which shows the structure of FF circuit. 6 is a timing chart illustrating the operation of the FF circuit. The figure which shows the state of the transistor which FF circuit has in each operation period. The figure which shows the state of the transistor which FF circuit has in each operation period. 6 is a timing chart for explaining the operation of the frequency divider circuit. The circuit diagram which shows the structure of FF circuit. The figure which shows the structure of a frequency divider circuit and FF circuit. The figure which shows an example of a structure and operation | movement of a general frequency divider. The circuit diagram explaining a circuit symbol and its circuit structure. The figure explaining the structure of CPU. 10 is a cross-sectional view illustrating a method for manufacturing a transistor. 10 is a cross-sectional view illustrating a method for manufacturing a transistor. 10 is a cross-sectional view illustrating a method for manufacturing a transistor. FIG. 10 is a cross-sectional view illustrating a structural example of a transistor. FIG. 10 is a cross-sectional view illustrating a structural example of a transistor. FIG. 14 illustrates an example of an electronic device. 3A and 3B illustrate a crystal structure of an oxide material. 3A and 3B illustrate a crystal structure of an oxide material. 3A and 3B illustrate a crystal structure of an oxide material. 3A and 3B illustrate a crystal structure of an oxide material. 6A and 6B illustrate gate voltage dependence of field-effect mobility obtained by calculation. 10A and 10B illustrate gate voltage dependence of drain current and field-effect mobility obtained by calculation. 10A and 10B illustrate gate voltage dependence of drain current and field-effect mobility obtained by calculation. 10A and 10B illustrate gate voltage dependence of drain current and field-effect mobility obtained by calculation. 4A and 4B illustrate a cross-sectional structure of a transistor used for calculation. 10 is a graph of transistor characteristics using an oxide semiconductor film. Shows a, _V g -I _d characteristics of the post a BT test of a transistor of Sample 1. Shows a, _V g -I _d characteristics of the after BT test of a transistor as the sample 2. The figure which shows the XRD spectrum of the sample A and the sample B. The figure which shows the relationship between the off-state current of a transistor, and the substrate temperature at the time of a measurement. The figure which shows _Vg dependence of _Id and field effect mobility. The figure which shows the relationship between a substrate temperature and a threshold voltage, and the relationship between a substrate temperature and field effect mobility.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

Note that the functions of “source” and “drain” may be interchanged when transistors having different polarities are employed or when the direction of current changes during circuit operation. Therefore, in this specification, the terms “source” and “drain” can be used interchangeably.

“Electrically connected” includes a case of being connected via “something having an electric action”. Here, the “having some electric action” is not particularly limited as long as it can exchange electric signals between the connection targets. For example, “thing having some electric action” includes electrodes, wiring, switching elements such as transistors, resistance elements, inductors, capacitors, and other elements having various functions.

Even in the case where independent components are illustrated as being electrically connected to each other on the circuit diagram, in practice, for example, when a part of the wiring also functions as an electrode, In some cases, the conductive film has the functions of a plurality of components. In this specification, the term “electrically connected” also includes such a case where one conductive film has functions of a plurality of components.

The position, size, range, and the like of each component illustrated in the drawings and the like may not represent the actual position, size, range, or the like for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like disclosed in the drawings and the like.

Ordinal numbers such as “first”, “second”, and “third” are attached to avoid confusion between components, and are not limited numerically.

The voltage refers to a potential difference between two points, and the potential refers to electrostatic energy (electric potential energy) possessed by a unit charge in an electrostatic field at a certain point. However, generally, a potential difference between a potential at a certain point and a reference potential (for example, ground potential) is simply referred to as a potential or a voltage, and the potential and the voltage are often used as synonyms. Therefore, in this specification, unless otherwise specified, the potential may be read as a voltage, or the voltage may be read as a potential.

(Embodiment 1)
An example of a structure and operation of the divider circuit which is one embodiment of the present invention is described with reference to FIGS. The frequency divider circuit has one or a plurality of FF (Flip Flop) circuits. In this embodiment, a frequency dividing circuit 200 including three FF circuits, which is illustrated by an FF circuit 201, an FF circuit 202, and an FF circuit 203, is described as an example.

FIG. 1A is a block diagram illustrating a configuration of the frequency dividing circuit 200, in which FF circuits 201 to 203 are connected in series in three stages.

Each of the FF circuits 201 to 203 includes a clock signal input unit CK, an input unit D, an output unit Q, and an output unit Q bar. In the FF circuit 201, the clock signal input unit CK is electrically connected to the terminal unit 211. A clock signal CLK having a specific frequency is input to the terminal portion 211. The clock signal CLK input to the terminal unit 211 is input to the FF circuit 201 via the clock signal input unit CK. The output part Q bar of the FF circuit 201 is electrically connected to the input part D of the FF circuit 201. The output unit Q of the FF circuit 201 is electrically connected to the clock signal input unit CK of the FF circuit 202 via the node 212. The output part Q bar of the FF circuit 202 is electrically connected to the input part D of the FF circuit 202. The output unit Q of the FF circuit 202 is electrically connected to the clock signal input unit CK of the FF circuit 203 via the node 213. The output part Q bar of the FF circuit 203 is electrically connected to the input part D of the FF circuit 203. The output unit Q of the FF circuit 203 is electrically connected to the terminal unit 214.

FIG. 1B is a circuit diagram illustrating a configuration of the FF circuit 201.

Note that in the drawing, a symbol “OS” is attached to a portion where an OS transistor is used.

An FF circuit 201 illustrated in FIG. 1B includes an inverter 221 (also referred to as a first inverter) and an inverter 222 (also referred to as a second inverter), and is also referred to as a p-type transistor 231 (also referred to as a first transistor). ), A transistor 234 (also referred to as a fifth transistor), an n-type transistor 232 (also referred to as a second transistor), a transistor 233 (also referred to as a third transistor), and a transistor 235 (also referred to as a sixth transistor). And a transistor 236 (also referred to as a seventh transistor), a transistor 237 (also referred to as a fourth transistor) which is an OS transistor, and a transistor 238 (also referred to as an eighth transistor).

A node 216 to which the terminal portion 211 and the input portion of the inverter 221 are connected corresponds to the clock signal input portion CK. Inverter 221 generates clock bar signal CLKB, which is an inverted signal of input clock signal CLK, and outputs it to node 215. One of a source and a drain of the transistor 231 is electrically connected to VDD, and the other of the source and the drain is electrically connected to the node 217. One of a source and a drain of the transistor 232 is electrically connected to the node 217. Gates of the transistors 231 and 232 are electrically connected to the node 216. One of a source and a drain of the transistor 233 is electrically connected to VSS, and the other of the source and the drain is electrically connected to the other of the source and the drain of the transistor 232. One of a source and a drain of the transistor 237 is electrically connected to the gate of the transistor 233 through the node 219, and the other of the source and the drain is electrically connected to the node 218. Inverter 222 has an input portion electrically connected to node 212 and an output portion electrically connected to node 218.

One of a source and a drain of the transistor 234 is electrically connected to VDD, and the other of the source and the drain is electrically connected to the node 212. One of a source and a drain of the transistor 235 is electrically connected to the node 212. The gates of the transistor 234 and the transistor 235 are electrically connected to the node 215. One of a source and a drain of the transistor 236 is electrically connected to VSS, and the other of the source and the drain is electrically connected to the other of the source and the drain of the transistor 235. One of a source and a drain of the transistor 238 is electrically connected to the gate of the transistor 236 through the node 220, and the other of the source and the drain is electrically connected to the node 217.

Next, the operation of the FF circuit 201 will be described with reference to FIGS. FIG. 3 is a timing chart for explaining the operation of the FF circuit 201, and shows the potential of each node in the operation period t1 to t4. 4 and 5 show the states of the transistors included in the FF circuit 201 in each operation period.

Note that the following description of the operation is not limited thereto, and if the conduction state of each transistor is the same, the conductivity type of each transistor, the combination of logic circuits, and the potential of each signal can be set as appropriate. Here, each signal is represented by an H potential and an L potential, the H potential is a potential that turns on the n-type transistor and the p-type transistor is turned off (for example, VDD), and the L potential is the state that the p-type transistor is turned on. The potential is set to turn off the n-type transistor (for example, VSS). Note that the potential of the node 219 is an H potential as an initial state, and the potential of the node 220 is an H potential as an initial state. Further, the clock signal CLK changes to an H potential or an L potential at a specific period (frequency). In FIGS. 4 and 5, an x mark is added to a transistor that is turned off.

First, the operation in the period t1 in FIG. 3 is described with reference to FIG.

In the period t1, the H potential of the clock signal CLK is input from the terminal portion 211, the potential of the node 216 becomes the H potential, the clock bar signal CLKB is generated by the inverter 221, and the potential of the node 215 becomes the L potential. Then, the transistor 237 is turned off, the H potential is held at the node 219, and the transistor 233 is also kept on.

Further, since the node 216 has an H potential, the transistor 231 is turned off, the transistor 232 is turned on, the node 217 and the node 223 are brought into conduction, and the node 217 is supplied with the L potential (VSS).

Further, since the potential of the node 215 is an L potential, the transistor 234 is turned on and the transistor 235 is turned off. Then, the H potential (VDD) is supplied to the node 212, the L potential is output from the inverter 222, and the node 218 becomes the L potential.

Further, the transistor 238 is turned on, the node 217 and the node 220 are brought into conduction, and the potential of the node 220 becomes the L potential. Thus, the transistor 236 is turned off.

Next, the operation in the period t2 in FIG. 3 is described with reference to FIG.

In the period t2, the L potential of the clock signal CLK is input from the terminal portion 211, the potential of the node 216 becomes the L potential, the clock bar signal CLKB is generated by the inverter 221, and the potential of the node 215 becomes the H potential. When the potential of the node 216 becomes an L potential, the transistor 238 and the transistor 232 are turned off, the transistor 231 is turned on, and the H potential is supplied to the node 217.

Since the transistor 238 is in an off state, the node 217 and the node 220 are not conducted, the potential of the node 220 is maintained at the L potential, and the transistor 236 is also maintained in the off state.

In addition, since the potential of the node 215 is H, the transistor 234 is turned off and the transistor 235 is turned on. However, since the transistor 236 is turned off, the node 212 is in an electrically floating state (floating state). Thus, the charge at the node 212 is held without being moved. Here, as a result, the node 212 holds the H potential. Therefore, the L potential is output from the inverter 222 to the node 218. Further, since the node 215 is at the H potential, the transistor 237 is turned on, the node 218 and the node 219 are brought into conduction, and the potential of the node 219 becomes the L potential. Accordingly, the transistor 233 is turned off.

Next, operation in the period t3 in FIG. 3 is described with reference to FIG.

In the period t3, the H potential of the clock signal CLK is input from the terminal portion 211, the potential of the node 216 becomes the H potential, the clock bar signal CLKB is generated by the inverter 221, and the potential of the node 215 becomes the L potential. When the potential of the node 215 becomes the L potential, the transistor 237 is turned off, the potential of the node 219 (L potential) is held, and the transistor 233 is also kept off.

Further, when the potential of the node 216 becomes an H potential, the transistor 232 is turned on and the transistor 231 is turned off. However, since the transistor 233 is turned off, the node 217 is in an electrically floating state (floating state). Thus, the charge at the node 217 is held without being moved. Here, as a result, the node 217 holds the H potential. Further, the transistor 238 is turned on, the node 217 and the node 220 are brought into conduction, and the potential of the node 220 becomes the H potential. Accordingly, the transistor 236 is turned on.

Since the potential of the node 215 becomes the L potential, the transistor 234 is turned on, the transistor 235 is turned off, the H potential is supplied to the node 212, the L potential is output from the inverter 222, and the node 218 becomes the L potential. .

Next, operation in the period t4 in FIG. 3 is described with reference to FIG.

In the period t4, the L potential of the clock signal CLK is input from the terminal portion 211, the potential of the node 216 becomes the L potential, the clock bar signal CLKB is generated by the inverter 221, and the potential of the node 215 becomes the H potential. When the potential of the node 216 becomes an L potential, the transistor 238 is turned off, the potential of the node 220 (H potential) is held, and the transistor 236 is also kept on.

Further, when the potential of the node 215 becomes an H potential, the transistor 234 is turned off, the transistor 235 is turned on, the node 212 and the node 223 are brought into conduction, and the node 212 is supplied with the L potential (VSS). When the L potential is supplied to the node 212, the H potential is output from the inverter 222, and the node 218 becomes the H potential.

Further, when the potential of the node 215 becomes H potential, the transistor 237 is turned on, the node 218 and the node 219 are brought into conduction, the node 219 becomes H potential, and the transistor 233 is turned on.

Further, when the potential of the node 216 becomes an L potential, the transistor 231 is turned on, the transistor 232 is turned off, and the node 217 becomes an H potential.

As described above, the FF circuit which is one embodiment of the present invention can output a signal having a half frequency of the input clock signal CLK. Further, although an example in which the potential of the node 212 is output as the output of the FF circuit is described in this embodiment, the potential of another node may be used as the output. For example, when the potential of the node 219 or the node 220 is used as an output, a signal having a duty ratio substantially the same as that of the input clock signal CLK and a half frequency can be output.

The FF circuit disclosed in this embodiment can be used for other circuits such as a counter circuit.

FIG. 6 is a timing chart for explaining the operation of the frequency dividing circuit 200, and shows changes with time of potentials in the terminal portion 211, the node 212, the node 213, and the terminal portion 214. The clock signal CLK input to the terminal unit 211 is output to the node 212 after the frequency is halved (the cycle is doubled) by the FF circuit 201.

Further, the clock signal CLK input to the terminal portion 211 is output to the node 213 after the frequency is 1/4 times (period is 4 times) by the FF circuit 201 and the FF circuit 202.

The clock signal CLK input to the terminal unit 211 is output to the terminal unit 114 after the frequency is 1/8 times (the cycle is 8 times) by the FF circuit 201, the FF circuit 202, and the FF circuit 203. As described above, the frequency of the clock signal CLK is halved every time one stage is passed through the FF circuit.

For example, when a clock signal CLK having a frequency of 32.768 kHz is input to a frequency dividing circuit in which 15 stages of FF circuits are connected in series, the clock signal CLK having a frequency of 1 Hz can be obtained. That is, the frequency dividing circuit 200 can also be used as a timer circuit that generates a signal at regular intervals.

The FF circuit which is one embodiment of the present invention can be configured with a smaller number of transistors than a conventional DFF circuit, and the number of inverters used is small. Therefore, an increase in power consumption due to through current can be suppressed. That is, a frequency divider circuit can be manufactured with a smaller number of transistors than in the past. Thus, a semiconductor device with a small occupation area and reduced power consumption can be realized.

The OS transistor is significantly lower than the off-state current of a transistor using silicon, and can have an off-current value per channel width of 1 μm of 100 zA or less, preferably 10 zA or less, and more preferably 1 zA or less.

That is, by using an OS transistor as the transistor 237, the potential of the node 219 can be stably maintained when the transistor 237 is turned off. In particular, when the number of connection stages of the FF circuit is increased, the time for holding the potential of the node 219 while the transistor 237 is turned off becomes longer, so that the effect becomes remarkable.

Similarly, by using an OS transistor as the transistor 238, the potential of the node 220 can be stably maintained when the transistor 238 is turned off.

An FF circuit 251 illustrated in FIG. 2A has a circuit configuration similar to that of the FF circuit 201 and is an FF circuit in which an OS transistor is used not only for the transistor 237 and the transistor 238 but also for the transistor 233 and the transistor 236. is there. Note that an OS transistor may be used as the transistor 232 or the transistor 235.

By using an OS transistor for one or both of the transistor 232 and the transistor 233, when the transistor 231 is turned on and the node 217 is set to the H potential, the charge of the node 217 is prevented from leaking to the node 223. Charge can be supplied efficiently. Therefore, power consumption can be reduced.

Further, when the number of connection stages of the FF circuit is increased, the time during which the H potential is held at the node 217 also increases. Therefore, by using an OS transistor for one or both of the transistor 232 and the transistor 233, the potential of the node 217 can be stably maintained. In particular, since the transistor 233 is off for a longer time than the transistor 232, an OS transistor is preferably used as the transistor 233.

In addition, when an OS transistor is used for either or both of the transistor 235 and the transistor 236, when the transistor 234 is turned on and the node 212 is set to the H potential, the charge of the node 212 leaks to the node 223. Thus, charge can be supplied efficiently. Therefore, power consumption can be reduced.

In addition, by using an OS transistor for one or both of the transistor 235 and the transistor 236, the potential of the node 212 can be stably maintained. In particular, since the transistor 236 is off for a longer time than the transistor 235, an OS transistor is preferably used as the transistor 236.

2B and 2C are circuit diagrams in which an OS transistor is used as a transistor included in the inverter. By using an OS transistor as a transistor constituting the inverter, power consumption can be further reduced.

By using an OS transistor as a transistor included in the semiconductor device, a semiconductor device with stable operation and high reliability can be realized. In addition, a semiconductor device with reduced power consumption can be realized.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 2)
In this embodiment, an FF circuit 261 having a structure different from that of the FF circuit 201 described in Embodiment 1 is described.

FIG. 7 is a circuit diagram showing a configuration of the FF circuit 261. The FF circuit 261 has a structure in which a capacitor 252 and a capacitor 253 are added to the node 212 and the node 217 of the FF circuit 201 described in Embodiment 1.

One electrode of the capacitor 252 included in the FF circuit 261 is electrically connected to the node 212, and the other electrode is electrically connected to a common electrode to which a common potential is supplied. In addition, one electrode of the capacitor 253 is electrically connected to the node 217, and the other electrode is electrically connected to a common electrode to which a common potential is supplied.

Here, an example in which a common potential is supplied to the other electrode of the capacitor 252 and the capacitor 253 is described; however, the potential supplied to the electrode may be a fixed potential, and may be VDD or VSS. Each may have a different potential.

By adding the capacitor 252 and the capacitor 253, the potential of the node 212 and the node 217 can be more stably maintained even when the node 212 and the node 217 are in a floating state. Therefore, the reliability of the semiconductor device can be further improved.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 3)
In this embodiment, a divider circuit 300 having a structure different from that of the divider circuit 200 described in the above embodiment is described. FIG. 8A is a block diagram illustrating a configuration of the frequency divider circuit 300, in which three stages of FF circuits 301 to 303 are connected in series.

Each of the FF circuits 301 to 303 includes a clock signal input unit CK, a clock bar signal input unit CK bar, an input unit D, an output unit Q, and an output unit Q bar. In the FF circuit 301, the clock signal input unit CK is electrically connected to the terminal unit 311.

A clock signal CLK having a specific frequency is input to the terminal portion 311. The clock signal CLK input to the terminal unit 311 is input to the FF circuit 301 via the clock signal input unit CK. The terminal unit 311 is connected to the clock bar signal input unit CK bar via the inverter 341. When the clock signal CLK is input to the terminal portion 311, a clock bar signal CLKB that is an inverted signal of the clock signal CLK is output from the inverter 341. The clock bar signal CLKB is input to the FF circuit 301 via the clock bar signal input unit CK bar.

The output unit Q of the FF circuit 301 is electrically connected to the clock signal input unit CK of the FF circuit 302 via the node 312. The output part Q bar of the FF circuit 301 is electrically connected to the input part D of the FF circuit 301 and the clock bar signal input part CK bar of the FF circuit 302.

The output unit Q of the FF circuit 302 is electrically connected to the clock signal input unit CK of the FF circuit 303 via the node 313. The output part Q bar of the FF circuit 302 is electrically connected to the input part D of the FF circuit 302 and the clock bar signal input part CK bar of the FF circuit 303. The output part Q of the FF circuit 303 is electrically connected to the terminal part 314. The output part Q bar of the FF circuit 303 is electrically connected to the input part D of the FF circuit 303.

FIG. 8B is a circuit diagram illustrating a configuration of the FF circuit 301.

A node 316 illustrated in FIG. 8B corresponds to the clock signal input portion CK. The node 315 corresponds to the clock bar signal input unit CK bar. The FF circuit 301 is different from the FF circuit 201 illustrated in FIG. 1B in that the inverter 221 is omitted and the clock bar signal CLKB is input from the outside. In the second and subsequent FF circuits, a signal output from the output section Q bar of the preceding FF circuit can be used as the clock bar signal CLKB.

In the FF circuit 301, since the inverter 221 is not formed, the occupied area can be reduced as compared with the FF circuit 201. That is, the frequency dividing circuit 300 can occupy a smaller area than the frequency dividing circuit 200. Since other circuit configurations and operation methods can be the same as those of the FF circuit 201, the description thereof is omitted.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 4)
In this embodiment, a structure of a CPU that is one of semiconductor devices according to one embodiment of the present invention will be described.

FIG. 11 shows the configuration of the CPU of this embodiment. The CPUs shown in FIG. / F9920. The ALU is an Arithmetic logic unit, the Bus / I / F is a bus interface, and the ROM / I / F is a ROM interface. The ROM 9909 and the ROM • I / F9920 may be provided in separate chips. Needless to say, the CPU illustrated in FIG. 11 is just an example in which the configuration is simplified, and an actual CPU may have various configurations depending on the application.

Instructions input to the CPU via the Bus I / F 9908 are input to the Instruction Decoder 9903, decoded, and then input to the ALU Controller 9902, Interrupt Controller 9904, Register Controller 9907, and Timer Control 9905.

The ALU / Controller 9902, the Interrupt / Controller 9904, the Register / Controller 9907, and the Timing / Controller 9905 perform various controls based on the decoded instructions. Specifically, the ALU / Controller 9902 generates a signal for controlling the operation of the ALU 9901. The Interrupt Controller 9904 determines and processes an interrupt request from an external input / output device or a peripheral circuit from the priority or mask state during execution of the CPU program. The Register Controller 9907 generates an address of the Register 9906, and reads and writes the Register 9906 according to the state of the CPU.

The Timing Controller 9905 includes the frequency dividing circuit having the configuration described in the above embodiment, and generates operation signals for the ALU 9901, ALU Controller 9902, Instruction Decoder 9903, Interrupt Controller 9904, and Register Controller 9907. For example, the Timing Controller 9905 includes an internal clock generation unit (frequency divider circuit) that generates an internal clock signal CLK2 based on the reference clock signal CLK1, and inputs the clock signal CLK2 to the various circuits.

By using the divider circuit described in the above embodiment for the structure of the CPU, the area occupied by the CPU can be reduced, and power consumption can be reduced.

In this embodiment, the CPU has been described as an example. However, the divider circuit of the present invention is not limited to the CPU, and can be applied to LSIs such as a microprocessor, an image processing circuit, a DSP, and an FPGA.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 5)
In this embodiment, an example of an OS transistor and a transistor in which silicon is used for a semiconductor layer in which a channel is formed is used as an example, and a structure and a manufacturing method of a transistor that can be applied to the FF circuit described in the above embodiment. This will be described with reference to cross-sectional views shown in FIGS.

As shown in FIG. 12A, an insulating film 701 and a semiconductor film 702 separated from a single crystal semiconductor substrate are formed over a substrate 700.

There is no particular limitation on a material that can be used as the substrate 700 as long as it has heat resistance enough to withstand heat treatment performed later. For example, as the substrate 700, a glass substrate, a quartz substrate, a semiconductor substrate, a ceramic substrate, or the like manufactured by a fusion method or a float method can be used. As the glass substrate, a glass substrate having a strain point of 730 ° C. or higher is preferably used when the temperature of the subsequent heat treatment is high.

In this embodiment, the case where the semiconductor film 702 is single crystal silicon is described as an example; however, the semiconductor film 702 includes an amorphous semiconductor, a single crystal semiconductor, a polycrystalline semiconductor, a microcrystal, and the like. A crystalline semiconductor such as a semiconductor can be used. Examples of the semiconductor material include silicon, germanium, silicon germanium, silicon carbide, and gallium arsenide.

Hereinafter, a method for manufacturing the transistor 732 is described. Note that a specific example of a method for manufacturing the single crystal semiconductor film 702 is briefly described. First, an ion beam made of ions accelerated by an electric field is injected into a bond substrate, which is a single-crystal semiconductor substrate, and the crystal structure is disturbed locally from the surface of the bond substrate to a region at a certain depth. An embrittled layer that is weakened is formed. The depth of the region where the embrittlement layer is formed can be adjusted by the acceleration energy of the ion beam and the incident angle of the ion beam. Then, the bond substrate and the substrate 700 over which the insulating film 701 is formed are attached to each other so that the insulating film 701 is sandwiched therebetween. In the bonding, after the bond substrate and the substrate 700 are overlapped, a part of the bond substrate and the substrate 700 is 1 N / cm ² or more and 500 N / cm ² or less, preferably 11 N / cm ² or more and 20 N / cm ² or less. Apply pressure. When pressure is applied, the bond substrate and the insulating film 701 start bonding from that portion, and finally, the bonding reaches the entire adhered surface. Next, by performing heat treatment, the microvoids existing in the embrittled layer are combined with each other, and the volume of the microvoids is increased. As a result, the single crystal semiconductor film which is part of the bond substrate in the embrittlement layer is separated from the bond substrate. The temperature of the heat treatment is set so as not to exceed the strain point of the substrate 700. Then, the semiconductor film 702 can be formed by processing the single crystal semiconductor film into a desired shape by etching or the like.

In order to control the threshold voltage, the semiconductor film 702 includes an impurity element imparting p-type conductivity such as boron, aluminum, or gallium, or an impurity element imparting n-type conductivity such as phosphorus or arsenic. May be added. The impurity element for controlling the threshold voltage may be added to the semiconductor film before being etched into a predetermined shape, or to the semiconductor film 702 after being etched into a predetermined shape. You can go. Further, an impurity element for controlling the threshold voltage may be added to the bond substrate. Alternatively, after adding an impurity element to the bond substrate to roughly adjust the threshold voltage, the semiconductor before etching into a predetermined shape to finely adjust the threshold voltage You may perform also with respect to the film | membrane or the semiconductor film 702 after etching into a predetermined shape.

Note that although an example in which a single crystal semiconductor film is used is described in this embodiment, the present invention is not limited to this structure. For example, a polycrystalline, microcrystalline, or amorphous semiconductor film formed over the insulating film 701 by using a vapor deposition method may be used, or the semiconductor film may be crystallized by a known technique. Known crystallization methods include a laser crystallization method using laser light and a crystallization method using a catalytic element. Alternatively, a crystallization method using a catalytic element and a laser crystallization method can be used in combination. Also, when using a substrate having excellent heat resistance such as quartz, a thermal crystallization method using an electric furnace, a lamp heating crystallization method using infrared light, a crystallization method using a catalytic element, about 950 ° C. Alternatively, a crystallization method combining the high-temperature heating methods may be used.

Next, as illustrated in FIG. 12B, after a gate insulating film 703 is formed over the semiconductor film 702, a mask 705 is formed over the gate insulating film 703, and an impurity element imparting conductivity is added to the semiconductor film 702. By adding to a part of the impurity region, the impurity region 704 is formed.

The gate insulating film 703 can be formed by oxidizing or nitriding the surface of the semiconductor film 702 by performing high-density plasma treatment, heat treatment, or the like. The high-density plasma treatment is performed using, for example, a rare gas such as He, Ar, Kr, or Xe and a mixed gas such as oxygen, nitrogen oxide, ammonia, nitrogen, or hydrogen. In this case, high-density plasma can be generated at a low electron temperature by exciting the plasma by introducing a microwave. By oxidizing or nitriding the surface of the semiconductor film with oxygen radicals (which may include OH radicals) or nitrogen radicals (which may include NH radicals) generated by such high-density plasma, An insulating film having a thickness of 20 nm, preferably 5 to 10 nm can be formed in contact with the semiconductor film. For example, nitrous oxide (N ₂ O) is diluted 1 to 3 times (flow rate ratio) with Ar, and 3 to 5 kW microwave (2.45 GHz) power is applied at a pressure of 10 to 30 Pa to apply a semiconductor. The surface of the film 702 is oxidized or nitrided. By this treatment, an insulating film having a thickness of 1 nm to 10 nm (preferably 2 nm to 6 nm) is formed. Further, nitrous oxide (N ₂ O) and silane (SiH ₄ ) are introduced, and 3-5 kW microwave (2.45 GHz) power is applied at a pressure of 10-30 Pa, and silicon oxynitride is formed by vapor phase growth. A film is formed to form a gate insulating film. A gate insulating film having a low interface state density and an excellent withstand voltage can be formed by combining a solid phase reaction and a reaction by a vapor deposition method.

Since the oxidation or nitridation of the semiconductor film by the high-density plasma treatment described above proceeds by a solid phase reaction, the interface state density between the gate insulating film 703 and the semiconductor film 702 can be extremely low. Further, by directly oxidizing or nitriding the semiconductor film 702 by high-density plasma treatment, variation in thickness of the insulating film to be formed can be suppressed. Also, when the semiconductor film has crystallinity, the surface of the semiconductor film is oxidized by solid phase reaction using high-density plasma treatment, so that the rapid oxidation only at the crystal grain boundary is suppressed and the uniformity is good. A gate insulating film having a low interface state density can be formed. A transistor formed by including an insulating film formed by high-density plasma treatment in part or all of a gate insulating film can suppress variation in characteristics.

Further, using a plasma CVD method or a sputtering method, silicon oxide, silicon nitride, silicon nitride oxide, silicon oxynitride, aluminum oxide, aluminum nitride, zirconium oxide, yttrium oxide, lanthanum oxide, cesium oxide, tantalum oxide, magnesium oxide, Hafnium oxide, hafnium silicate (HfSi _x O _y (x> 0, y> 0)), nitrogen-added hafnium silicate (HfSi _x O _y (x> 0, y> 0)), nitrogen-added hafnium The gate insulating film 703 may be formed by a single layer or a stack of films including aluminate (HfAl _x O _y (x> 0, y> 0)) or the like.

Note that in this specification, oxynitride is a substance having a higher oxygen content than nitrogen in the composition, and nitride oxide has a nitrogen content higher than oxygen in the composition. Means a substance.

The thickness of the gate insulating film 703 can be, for example, 1 nm to 100 nm, preferably 10 nm to 50 nm. In this embodiment, a single-layer insulating film containing silicon oxide is used as the gate insulating film 703 by a plasma CVD method.

Next, after removing the mask 705, as shown in FIG. 12C, after removing part of the gate insulating film 703 and forming an opening 706 in a region overlapping with the impurity region 704 by etching or the like, A gate electrode 707 and a conductive film 708 are formed.

The gate electrode 707 and the conductive film 708 can be formed by forming a conductive film so as to cover the opening 706 and then processing the conductive film into a predetermined shape. The conductive film 708 is in contact with the impurity region 704 in the opening 706. For the formation of the conductive film, a CVD method, a sputtering method, a vapor deposition method, a spin coating method, or the like can be used. The conductive film is made of tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu), chromium (Cr), niobium (Nb), magnesium (Mg). Etc. can be used. An alloy containing the above metal as a main component may be used, or a compound containing the above metal may be used. Alternatively, the semiconductor film may be formed using a semiconductor such as polycrystalline silicon doped with an impurity element such as phosphorus which imparts conductivity.

Note that although the gate electrode 707 and the conductive film 708 are formed using a single-layer conductive film in this embodiment, this embodiment is not limited to this structure. The gate electrode 707 and the conductive film 708 may be formed using a plurality of stacked conductive films.

As a combination of the two conductive films, tantalum nitride or tantalum can be used for the first layer and tungsten can be used for the second layer. In addition to the above examples, tungsten nitride and tungsten, molybdenum nitride and molybdenum, aluminum and tantalum, aluminum and titanium, and the like can be given. Since tungsten and tantalum nitride have high heat resistance, heat treatment for thermal activation can be performed in the step after forming the two-layer conductive film. Further, as a combination of two conductive films, for example, silicon and nickel silicide doped with an impurity element imparting n-type conductivity, silicon and tungsten silicide doped with an impurity element imparting n-type conductivity Etc. can also be used.

In the case of a three-layer structure in which three conductive films are stacked, a stacked structure of a molybdenum film, an aluminum film, and a molybdenum film is preferably employed.

In addition, a light-transmitting oxide such as indium oxide, indium tin oxide mixture, indium zinc oxide mixture, zinc oxide, zinc aluminum oxide, zinc aluminum oxynitride, or zinc gallium oxide is formed over the gate electrode 707 and the conductive film 708. A conductive film can also be used.

Note that the gate electrode 707 and the conductive film 708 may be selectively formed by a droplet discharge method without using a mask. The droplet discharge method means a method of forming a predetermined pattern by discharging or ejecting droplets containing a predetermined composition from the pores, and includes an ink jet method and the like in its category.

The gate electrode 707 and the conductive film 708 are formed by using a dry etching method using inductively coupled plasma (ICP) after forming the conductive film, and etching conditions (power applied to the coil-type electrode layer). By appropriately adjusting the amount, the amount of electric power applied to the electrode layer on the substrate side, the electrode temperature on the substrate side, etc., etching can be performed to have a desired tapered shape. Further, the taper shape can control the angle and the like depending on the shape of the mask. As an etching gas, a chlorine-based gas such as chlorine, boron chloride, silicon chloride, or carbon tetrachloride, a fluorine-based gas such as carbon tetrafluoride, sulfur fluoride, or nitrogen fluoride, or oxygen can be used as appropriate. .

Next, as illustrated in FIG. 12D, an impurity element imparting one conductivity is added to the semiconductor film 702 using the gate electrode 707 and the conductive film 708 as masks, so that a channel formation region 710 overlapping with the gate electrode 707 is formed. A pair of impurity regions 709 sandwiching the channel formation region 710 and an impurity region 711 in which an impurity element is further added to part of the impurity region 704 are formed in the semiconductor film 702.

In this embodiment, the case where an impurity element imparting p-type conductivity (eg, boron) is added to the semiconductor film 702 is described as an example.

Next, as illustrated in FIG. 13A, an insulating film 712 and an insulating film 713 are formed so as to cover the gate insulating film 703, the gate electrode 707, and the conductive film 708. Specifically, the insulating films 712 and 713 include silicon oxide, silicon nitride, silicon nitride oxide, silicon oxynitride, aluminum nitride, aluminum oxide, aluminum nitride oxide, aluminum oxynitride, hafnium oxide, zirconium oxide, and yttrium oxide. A single layer or a stack of inorganic insulating films such as lanthanum oxide, cesium oxide, tantalum oxide, or magnesium oxide can be used. Note that the use of a low dielectric constant (low-k) material for the insulating films 712 and 713 enables a sufficient reduction in capacitance due to overlapping of various electrodes and wirings. Note that a porous insulating film using any of the above materials may be used for the insulating films 712 and 713. A porous insulating film has a lower dielectric constant than a high-density insulating film, so that parasitic capacitance caused by electrodes and wirings can be further reduced.

In this embodiment, the case where silicon oxynitride is used for the insulating film 712 and silicon nitride oxide is used for the insulating film 713 is described as an example. Further, although the case where the insulating film 712 and the insulating film 713 are formed over the gate electrode 707 and the conductive film 708 is illustrated in this embodiment mode, the present invention is insulated over the gate electrode 707 and the conductive film 708. Only one layer may be formed, or a plurality of three or more insulating films may be stacked.

Next, as illustrated in FIG. 13B, the surfaces of the gate electrode 707 and the conductive film 708 are exposed by performing CMP (chemical mechanical polishing) treatment or etching treatment on the insulating film 712 and the insulating film 713. Note that the surfaces of the insulating film 712 and the insulating film 713 are preferably as flat as possible in order to improve characteristics of the transistor 731 to be formed later.

Through the above steps, the transistor 732 can be formed.

Next, a method for manufacturing the transistor 731 is described. First, as illustrated in FIG. 13C, the oxide semiconductor layer 716 is formed over the insulating film 712 or the insulating film 713.

The oxide semiconductor layer 716 can be formed by processing an oxide semiconductor film formed over the insulating film 712 and the insulating film 713 into a desired shape. Specifically, a resist mask corresponding to a pattern shape to be processed is formed on the oxide semiconductor film using a known technique such as a photolithography method or an inkjet method, and a known method such as a dry etching method or a wet etching method is formed. The oxide semiconductor layer 716 may be formed by selectively removing unnecessary portions of the oxide semiconductor film using a technique.

The oxide semiconductor film can be formed by a sputtering method, an evaporation method, a PCVD method, a PLD method, an ALD method, an MBE method, or the like. The thickness of the oxide semiconductor film is 2 nm to 200 nm, preferably 3 nm to 50 nm, more preferably 3 nm to 20 nm.

In the case where the oxide semiconductor film is formed by a sputtering method, for example, a metal oxide containing In and Zn can be used as a target. As a sputtering gas, a rare gas (eg, argon), oxygen, or a mixed gas of a rare gas and oxygen can be used. In the case where a mixed gas of a rare gas and oxygen is used as the sputtering gas, the oxygen gas ratio is set to 30% by volume or more, preferably 50% by volume or more, and more preferably 80% by volume or more. Note that as the oxide semiconductor film is thinner, the short channel effect of the transistor is reduced. However, if the thickness is too thin, the influence of interface scattering becomes strong, and field effect mobility may be lowered.

Note that before the oxide semiconductor film is formed by a sputtering method, reverse sputtering that generates plasma by introducing argon gas is performed to remove dust attached to the surfaces of the insulating films 712 and 713. Is preferred. Reverse sputtering is a method of modifying the surface by forming a plasma near the substrate by applying a voltage using an RF power source on the substrate side in an argon atmosphere without applying a voltage to the target side. Note that nitrogen, helium, or the like may be used instead of the argon atmosphere. Alternatively, an argon atmosphere may be used in which oxygen, nitrous oxide, or the like is added. Alternatively, the reaction may be performed in an atmosphere in which chlorine, carbon tetrafluoride, or the like is added to an argon atmosphere.

As the oxide semiconductor, a material containing at least indium (In) or zinc (Zn) is preferably used. In addition, it is preferable that gallium (Ga) be included in addition to the stabilizer for reducing variation in electrical characteristics of the transistor including the oxide semiconductor. Moreover, it is preferable to have tin (Sn) as a stabilizer. Moreover, it is preferable to have hafnium (Hf) as a stabilizer. Moreover, it is preferable to have aluminum (Al) as a stabilizer.

As other stabilizers, lanthanoids such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb) , Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or lutetium (Lu).

For example, as an oxide semiconductor, indium oxide, tin oxide, zinc oxide, binary metal oxides such as In—Zn oxide, Sn—Zn oxide, Al—Zn oxide, Zn—Mg oxide Oxides, Sn—Mg oxides, In—Mg oxides, In—Ga oxides, In—Ga—Zn oxides (also referred to as IGZO) which are oxides of ternary metals, In— Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide, Al-Ga-Zn oxide, Sn-Al-Zn oxide, In-Hf-Zn oxide In-La-Zn-based oxide, In-Ce-Zn-based oxide, In-Pr-Zn-based oxide, In-Nd-Zn-based oxide, In-Sm-Zn-based oxide, In-Eu -Zn oxide, In-Gd-Zn oxide, In-Tb-Zn oxide, n-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In-Tm-Zn-based oxide, In-Yb-Zn-based oxide, In-Lu-Zn -Based oxides, In-Sn-Ga-Zn-based oxides that are oxides of quaternary metals, In-Hf-Ga-Zn-based oxides, In-Al-Ga-Zn-based oxides, In-Sn- An Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide can be used. In addition, SiO ₂ may be included in the oxide semiconductor.

Note that here, for example, an In—Ga—Zn-based oxide means an oxide containing In, Ga, and Zn as its main components, and there is no limitation on the ratio of In, Ga, and Zn. Moreover, metal elements other than In, Ga, and Zn may be contained.

Alternatively, a material represented by InMO ₃ (ZnO) _m (m> 0) may be used as the oxide semiconductor. Note that M represents one metal element or a plurality of metal elements selected from Sn, Zn, Ga, Fe, Mn, and Co. Alternatively, a material represented by In ₂ SnO ₅ (ZnO) _n (n> 0) may be used as the oxide semiconductor.

For example, an In—Ga—Zn-based oxide having an atomic ratio of In: Ga: Zn = 1: 1: 1 or In: Ga: Zn = 2: 2: 1 or an oxide in the vicinity of the composition is used. it can. Alternatively, In: Sn: Zn = 1: 1: 1, In: Sn: Zn = 2: 1: 3, or In: Sn: Zn = 2: 1: 5 atomic ratio In—Sn—Zn-based oxide Or an oxide in the vicinity of the composition may be used.

However, the composition is not limited thereto, and a material having an appropriate composition may be used depending on required semiconductor characteristics (field effect mobility, threshold value, variation, and the like). In order to obtain the required semiconductor characteristics, it is preferable that the carrier concentration, impurity concentration, defect density, atomic ratio of metal element to oxygen, interatomic bond distance, density, and the like are appropriate.

For example, high field-effect mobility can be obtained relatively easily with an In—Sn—Zn-based oxide. However, field-effect mobility can be increased by reducing the defect density in the bulk also in the case of using an In—Ga—Zn-based oxide.

Note that, for example, an oxide having an atomic ratio of In, Ga, and Zn of In: Ga: Zn = a: b: c (a + b + c = 1) and an atomic ratio of In: Ga: Zn = A: B: When the composition of the oxide of C (A + B + C = 1) is in the vicinity, a, b, c are
(A−A) ² + (b−B) ² + (c−C) ² ≦ r ²
Say to meet. For example, r may be 0.05. The same applies to other oxides.

In the case where an In—Zn-based oxide is used as the oxide semiconductor, the atomic ratio is In / Zn = 0.5 to 50, preferably In / Zn = 1 to 20, and more preferably In / Zn = 1. 5-15. By setting the atomic ratio of Zn within the preferable range, the field effect mobility of the transistor can be improved. Here, when the atomic ratio of the compound is In: Zn: O = X: Y: Z, Z> 1.5X + Y.

In this embodiment, a 30-nm-thick In—Ga—Zn-based oxide thin film obtained by a sputtering method using a metal oxide target containing In (indium), Ga (gallium), and Zn (zinc) Is used as an oxide semiconductor film. As the target, for example, the composition ratio of each metal is an atomic ratio of In: Ga: Zn = 1: 1: 0.5, In: Ga: Zn = 1: 1: 1, or In: Ga: Zn = A target that is 1: 1: 2 can be used. The relative density of the metal oxide target for forming the oxide semiconductor is 90% to 100%, preferably 95% to less than 100%. By using a target with high relative density, the formed oxide semiconductor film becomes a dense film. Note that the In—Ga—Zn-based oxide can be referred to as IGZO.

In the case where an In—Sn—Zn-based oxide thin film is used as the oxide semiconductor film, a composition ratio of a target for forming an In—Sn—Zn-based oxide by a sputtering method is set such that In: Sn: Zn is an atom. The number ratio may be 1: 2: 2, 2: 1: 3, 1: 1: 1, 20:45:35, or the like.

Note that in the case where an oxide semiconductor film is formed using a target containing In (indium) and Zn (zinc), the atomic ratio of the target is In / Zn of 0.5 to 50, preferably 1 to 20 More preferably, it should be 1.5 or more and 15 or less. By keeping the ratio of Zn in the above range, it is possible to improve field effect mobility.

In this embodiment mode, a substrate is held in a deposition chamber that is kept under reduced pressure, a sputtering gas from which hydrogen and water have been removed is introduced while residual moisture in the deposition chamber is removed, and oxidation is performed using the target. A physical semiconductor film is formed. It is preferable to use a highly purified gas as the sputtering gas. For example, when argon is used as the sputtering gas, a purity of 9 N, a dew point of −121 ° C., a content of H ₂ O of 0.1 ppb or less, and a content of H ₂ of 0.5 ppb or less are preferable. -112 ° C., _{H 2} O containing amount 1ppb or less, preferably the content of _{H 2} 1ppb.

In the oxide semiconductor film, oxygen is preferably excessive with respect to the stoichiometric ratio of the oxide semiconductor. When oxygen is excessive, generation of carriers due to oxygen vacancies in the oxide semiconductor can be suppressed.

At the time of film formation, the substrate temperature may be 100 ° C. or higher and 600 ° C. or lower, preferably 200 ° C. or higher and 400 ° C. or lower. By forming the film while heating the substrate, the concentration of impurities contained in the formed oxide semiconductor film can be reduced. Further, damage due to sputtering is reduced. In order to remove moisture remaining in the deposition chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. When the gas in the deposition chamber is exhausted using a cryopump, for example, a hydrogen atom, a compound containing a hydrogen atom such as water (H ₂ O) (more preferably a compound containing a carbon atom), or the like is exhausted. The concentration of impurities contained in the oxide semiconductor film formed in the deposition chamber can be reduced.

As an example of the film formation conditions, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power source is 0.5 kW, and oxygen is used as the sputtering gas (oxygen flow rate ratio: 100%). The Note that a pulse direct current (DC) power source is preferable because dust generated in film formation can be reduced and the film thickness can be made uniform.

In addition, by setting the leak rate in the film formation chamber of the sputtering apparatus to 1 × 10 ⁻¹⁰ Pa · m ³ / second or less, alkali metal, hydride, or the like on the oxide semiconductor film during film formation by the sputtering method is used. Impurity contamination can be reduced. Further, by using the above-described adsorption-type vacuum pump as an exhaust system, backflow of impurities such as alkali metal, hydrogen atom, hydrogen molecule, water, hydroxyl group, or hydride from the exhaust system can be reduced.

In addition, when the purity of the target is 99.99% or higher, alkali metals, hydrogen atoms, hydrogen molecules, water, hydroxyl groups, hydrides, or the like mixed in the oxide semiconductor film can be reduced. In addition, when the target is used, the concentration of alkali metal such as lithium, sodium, or potassium can be reduced in the oxide semiconductor film.

Note that in order to prevent the oxide semiconductor film from containing hydrogen, a hydroxyl group, and water as much as possible, a substrate in which the insulating film 712 and the insulating film 713 are formed in a preheating chamber of a sputtering apparatus as a pretreatment for film formation. It is preferable to preheat 700 and desorb and exhaust impurities such as water or hydrogen adsorbed on the substrate 700. Note that the preheating temperature is 100 ° C. or higher and 400 ° C. or lower, preferably 150 ° C. or higher and 300 ° C. or lower. In addition, a cryopump is preferable as the exhaust means provided in the preheating chamber. Note that this preheating treatment can be omitted. Further, this preheating may be similarly performed on the substrate 700 over which the conductive films 719 and 720 are formed before the gate insulating film 721 to be formed later.

Note that etching for forming the oxide semiconductor layer 716 may be dry etching or wet etching, or both of them may be used. As an etching gas used for dry etching, a gas containing chlorine (chlorine-based gas such as chlorine (Cl ₂ ), boron trichloride (BCl ₃ ), silicon tetrachloride (SiCl ₄ ), carbon tetrachloride (CCl ₄ ), or the like) Is preferred. Gas containing fluorine (fluorine-based gas such as carbon tetrafluoride (CF ₄ ), sulfur hexafluoride (SF ₆ ), nitrogen trifluoride (NF ₃ ), trifluoromethane (CHF ₃ ), etc.), bromide Hydrogen (HBr), oxygen (O ₂ ), a gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases, or the like can be used.

As the dry etching method, a reactive ion etching (RIE) method can be used. In addition, as a plasma source, capacitively coupled plasma (CCP), inductively coupled plasma (ICP), electron cyclotron resonance (ECR), helicon wave H plasma, helicon wave H plasma, and helicon wave H plasma. Wave Plasma), microwave excitation surface wave plasma SWP (Surface Wave Plasma), or the like can be used. When etching is performed by a dry etching method, the etching conditions (the amount of power applied to the coil-type electrode, the amount of power applied to the electrode on the substrate side, the electrode temperature on the substrate side, etc.) so that the desired shape can be etched. ) As appropriate.

As an etchant used for wet etching, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or an organic acid such as citric acid or oxalic acid can be used. In this embodiment, ITO-07N (manufactured by Kanto Chemical Co., Inc.) is used.

A resist mask for forming the oxide semiconductor layer 716 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Note that before the conductive film in the next step is formed, reverse sputtering is preferably performed to remove a resist residue or the like attached to the surfaces of the oxide semiconductor layer 716, the insulating film 712, and the insulating film 713.

Note that an oxide semiconductor film formed by sputtering or the like may contain a large amount of water or hydrogen (including a hydroxyl group) as an impurity. Water or hydrogen is an impurity for an oxide semiconductor because it easily forms a donor level. Therefore, in one embodiment of the present invention, in order to reduce (dehydrate or dehydrogenate) an impurity such as water or hydrogen in the oxide semiconductor film, the oxide semiconductor layer 716 is subjected to nitrogen or nitrogen in a reduced pressure atmosphere. Moisture content when measured using an inert gas atmosphere such as a rare gas, an oxygen gas atmosphere, or an ultra-dry air (CRDS (cavity ring down laser spectroscopy) type dew point meter) is 20 ppm (-55 in terms of dew point) ° C) or less, preferably 1 ppm or less, preferably 10 ppb or less of air) under an atmosphere.

By performing heat treatment on the oxide semiconductor layer 716, water or hydrogen in the oxide semiconductor layer 716 can be eliminated. Specifically, heat treatment may be performed at a temperature of 250 ° C. to 750 ° C., preferably 400 ° C. to less than the strain point of the substrate. For example, it may be performed at 500 ° C. for about 3 minutes to 6 minutes. When the RTA method is used for the heat treatment, dehydration or dehydrogenation can be performed in a short time. Therefore, even when a glass substrate is used as the substrate, the treatment can be performed at a temperature exceeding the strain point of the glass substrate.

In this embodiment, an electric furnace which is one of heat treatment apparatuses is used.

Note that the heat treatment apparatus is not limited to an electric furnace, and may include a device for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

In the heat treatment, it is preferable that water or hydrogen is not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm). Or less, preferably 0.1 ppm or less).

Through the above steps, the concentration of hydrogen in the oxide semiconductor layer 716 can be reduced and the oxide semiconductor layer 716 can be highly purified.

After the oxide semiconductor layer 716 is formed, oxygen may be introduced into the oxide semiconductor layer 716 by an ion implantation method. Further, oxygen may be introduced by a plasma doping method. Specifically, oxygen is turned into plasma using radio frequency (RF), and oxygen radicals and oxygen ions are introduced into the oxide semiconductor layer 716. At this time, it is preferable to apply a bias to the substrate over which the oxide semiconductor layer 716 is formed. By increasing the bias applied to the substrate, oxygen can be introduced deeper.

Oxygen (oxygen radicals, oxygen atoms, and / or oxygen ions) introduced into the oxide semiconductor layer 716 by a plasma doping method may be supplied from a plasma generator using a gas containing oxygen, or ozone is generated. It may be supplied by the device.

After introducing oxygen into the oxide semiconductor layer 716, heat treatment (preferably 200 ° C. to 600 ° C., for example, 250 ° C. to 550 ° C.) may be performed. For example, heat treatment is performed at 450 ° C. for 1 hour in a nitrogen atmosphere. Note that it is preferable that the atmosphere does not contain water, hydrogen, or the like.

Oxygen that is one of the main components of the oxide semiconductor that is simultaneously reduced by the impurity removal step due to the introduction of oxygen into the oxide semiconductor layer 716 and heat treatment, and the oxide semiconductor layer 716 is i-type. Can be (intrinsic).

The oxide semiconductor may be single crystal or non-single crystal. In the latter case, it may be amorphous or polycrystalline. Moreover, the structure which contains the part which has crystallinity in an amorphous may be sufficient, and a non-amorphous may be sufficient.

Since an oxide semiconductor in an amorphous state can obtain a flat surface relatively easily, interface scattering when a transistor is manufactured using the oxide semiconductor can be reduced, and relatively high field-effect mobility can be achieved. Can be obtained.

In addition, in an oxide semiconductor having crystallinity, defects in a bulk can be further reduced, and field effect mobility higher than that of an oxide semiconductor in an amorphous state can be obtained by increasing surface flatness. In order to improve the flatness of the surface, it is preferable to form an oxide semiconductor on the flat surface. Specifically, the average surface roughness (Ra) is 1 nm or less, preferably 0.3 nm or less, more preferably Is preferably formed on a surface of 0.1 nm or less. Ra can be evaluated with an atomic force microscope (AFM).

In the case where an oxide semiconductor having crystallinity is used for the oxide semiconductor layer 716, the insulating film 713 in contact with the oxide semiconductor layer 716 may have sufficient flatness so that the oxide semiconductor can easily grow. preferable. Further, an insulating film having sufficient flatness may be provided between the insulating film 713 and the oxide semiconductor layer 716.

As an oxide semiconductor having crystallinity, the c-axis-oriented and triangular or hexagonal atomic arrangement as viewed from the ab plane, the surface, or the interface direction, and metal atoms are layered or metal atoms in the c-axis And oxygen atoms are arranged in layers, and the ab or b-axis direction of the ab plane is different (rotated around the c-axis) crystal semiconductor (CAAC-OS: C Axis Aligned Crystalline Oxide) It is preferable to use a semiconductor).

CAAC-OS is a non-single crystal in a broad sense, and has a triangular, hexagonal, equilateral triangle, or equilateral hexagonal atomic arrangement when viewed from the direction perpendicular to the ab plane, and is perpendicular to the c-axis direction. When viewed from the right direction, it includes a phase in which metal atoms are arranged in layers, or metal atoms and oxygen atoms are arranged in layers.

A CAAC-OS is not a single crystal but is not formed of only an amorphous substance. Further, although the CAAC-OS includes a crystallized portion (crystal portion), the boundary between one crystal portion and another crystal portion may not be clearly distinguished.

Part of oxygen included in the CAAC-OS may be replaced with nitrogen. In addition, the c-axis of each crystal part included in the CAAC-OS may be aligned in a certain direction (eg, a direction perpendicular to a substrate surface on which the CAAC-OS is formed, the surface of the CAAC-OS, or the like). Alternatively, the normal line of the ab plane of each crystal part included in the CAAC-OS faces a certain direction (for example, a direction perpendicular to the substrate surface on which the CAAC-OS is formed, the surface of the CAAC-OS, or the like). Also good.

The CAAC-OS can be a conductor or an insulator depending on its composition or the like. Further, it is transparent or opaque to visible light depending on its composition.

As an example of such a CAAC-OS, a triangular or hexagonal atomic arrangement is observed when observed from a direction perpendicular to the film surface or a supporting substrate surface, and metal atoms are observed when the film cross section is observed. Alternatively, an oxide in which a layered arrangement of metal atoms and oxygen atoms (or nitrogen atoms) is recognized can be given.

An example of a crystal structure included in the CAAC-OS will be described in detail with reference to FIGS. Unless otherwise specified, in FIGS. 18 to 20, the upper direction is the c-axis direction, and the plane orthogonal to the c-axis direction is the ab plane. Note that the upper half and the lower half simply refer to the upper half and the lower half when the ab surface is used as a boundary. In FIG. 18, O surrounded by a circle represents tetracoordinate O and O surrounded by a double circle represents tricoordinate O.

FIG. 18A illustrates a structure including one hexacoordinate In atom and six tetracoordinate oxygen atoms adjacent to In (hereinafter, tetracoordinate O). Here, a structure in which only one oxygen atom is adjacent to one metal atom is referred to as a small group. The structure in FIG. 18A has an octahedral structure, but is illustrated as a planar structure for simplicity. Note that three tetracoordinate O atoms exist in each of an upper half and a lower half in FIG. In the small group illustrated in FIG. 18A, electric charge is 0.

FIG. 18B illustrates one pentacoordinate Ga, three tricoordinate oxygen atoms close to Ga (hereinafter, tricoordinate O), and two tetracoordinates close to Ga. And a structure having O. All tricoordinate O atoms are present on the ab plane. One tetracoordinate O atom exists in each of an upper half and a lower half in FIG. In addition, since In also has five coordination, the structure illustrated in FIG. 18B can be employed. In the small group illustrated in FIG. 18B, electric charge is 0.

FIG. 18C illustrates a structure including one tetracoordinate Zn and four tetracoordinate O adjacent to Zn. In FIG. 18C, there is one tetracoordinate O in the upper half, and three tetracoordinate O in the lower half. Alternatively, three tetracoordinate O atoms may exist in the upper half of FIG. 18C and one tetracoordinate O atom may exist in the lower half. In the small group illustrated in FIG. 18C, electric charge is 0.

FIG. 18D illustrates a structure including one hexacoordinate Sn and six tetracoordinate O adjacent to Sn. In FIG. 18D, there are three tetracoordinate O atoms in the upper half and three tetracoordinate O atoms in the lower half. In the small group illustrated in FIG. 18D, electric charge is +1.

FIG. 18E illustrates a small group including two Zn atoms. In FIG. 18E, there is one tetracoordinate O in the upper half, and one tetracoordinate O in the lower half. In the small group illustrated in FIG. 18E, electric charge is -1.

Here, an aggregate of a plurality of small groups is referred to as a medium group, and an aggregate of a plurality of medium groups is referred to as a large group (also referred to as a unit cell).

Here, a rule for combining these small groups will be described. The three O atoms in the upper half of 6-coordinate In shown in FIG. 18A each have three adjacent Ins in the downward direction, and the three Os in the lower half each have three adjacent in the upper direction. In. One O in the upper half of the five-coordinate Ga shown in FIG. 18B has one adjacent Ga in the lower direction, and one O in the lower half has one adjacent Ga in the upper direction. Have. One O in the upper half of the tetracoordinate Zn shown in FIG. 18C has one neighboring Zn in the lower direction, and three Os in the lower half each have three neighboring Zn in the upper direction. Have In this way, the number of upward tetracoordinate O atoms of a metal atom is equal to the number of adjacent metal atoms in the downward direction of the O, and similarly the number of downward tetracoordinate O atoms of the metal atom is , The number of adjacent metal atoms in the upper direction of O is equal. Since O is 4-coordinate, the sum of the number of adjacent metal atoms in the downward direction and the number of adjacent metal atoms in the upward direction is 4. Therefore, when the sum of the number of tetracoordinate O atoms in the upward direction of a metal atom and the number of tetracoordinate O atoms in the downward direction of another metal atom is four, Small groups can be joined together. The reason is as follows. For example, in the case where a hexacoordinate metal atom (In or Sn) is bonded via tetracoordinate O in the lower half, since there are three tetracoordinate O atoms, a pentacoordinate metal atom (Ga or In) or a tetracoordinate metal atom (Zn).

The metal atoms having these coordination numbers are bonded via tetracoordinate O in the c-axis direction. In addition, a plurality of small groups are combined to form a middle group so that the total charge of the layer structure becomes zero.

FIG. 19A is a model diagram of a middle group that forms a layer structure of an In—Sn—Zn-based oxide. FIG. 19B illustrates a large group including three medium groups. Note that FIG. 19C illustrates an atomic arrangement in the case where the layered structure in FIG. 19B is observed from the c-axis direction.

In FIG. 19A, for the sake of simplicity, tricoordinate O is omitted and only tetracoordinate O is shown. For example, three tetracoordinates are provided in each of the upper half and the lower half of Sn. The presence of O is shown as 3 in a round frame. Similarly, in FIG. 19A, one tetracoordinate O atom exists in each of the upper half and the lower half of In, which is shown as 1 in a round frame. Similarly, in FIG. 19A, the lower half has one tetracoordinate O, the upper half has three tetracoordinate O, and the upper half has one. In the lower half, Zn having three tetracoordinate O atoms is shown.

In FIG. 19A, the middle group that forms the layer structure of the In—Sn—Zn-based oxide includes four tetracoordinate O atoms in the upper half and the lower half in order from the top. Are bonded to In in the upper and lower halves one by one, and the In is bonded to Zn having three tetracoordinate O atoms in the upper half. A small group consisting of two Zn atoms with four tetracoordinate O atoms in the upper half and the lower half through Coordinate O, and the In is composed of two Zn atoms with one tetracoordinate O atom in the upper half. In this configuration, three tetracoordinate O atoms are bonded to Sn in the upper and lower halves through one tetracoordinate O atom in the lower half of the small group. A plurality of medium groups are combined to form a large group.

Here, in the case of tricoordinate O and tetracoordinate O, the charges per bond can be considered to be −0.667 and −0.5, respectively. For example, the charges of In (6-coordinate or 5-coordinate), Zn (4-coordinate), and Sn (5-coordinate or 6-coordinate) are +3, +2, and +4, respectively. Therefore, the small group including Sn has a charge of +1. Therefore, in order to form a layer structure including Sn, a charge −1 that cancels the charge +1 is required. As a structure with charge −1, a small group including two Zn atoms can be given as illustrated in FIG. For example, if there is one small group containing Sn and one small group containing 2 Zn, the charge is canceled out, so the total charge of the layer structure can be zero.

Specifically, the large group illustrated in FIG. 19B is repeated, whereby an In—Sn—Zn-based oxide crystal (In ₂ SnZn ₃ O ₈ ) can be obtained. Note that the layer structure of the obtained In—Sn—Zn-based oxide can be represented by a composition formula, In ₂ SnZn ₂ O ₇ (ZnO) _m (m is 0 or a natural number).

In addition, an In—Sn—Ga—Zn-based oxide, which is an oxide of a quaternary metal, and an In—Ga—Zn-based oxide, which is an oxide of a ternary metal (also referred to as IGZO). In-Al-Zn-based oxide, Sn-Ga-Zn-based oxide, Al-Ga-Zn-based oxide, Sn-Al-Zn-based oxide, In-Hf-Zn-based oxide, In -La-Zn oxide, In-Ce-Zn oxide, In-Pr-Zn oxide, In-Nd-Zn oxide, In-Sm-Zn oxide, In-Eu-Zn oxide Oxide, In-Gd-Zn-based oxide, In-Tb-Zn-based oxide, In-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In- Tm-Zn-based oxides, In-Yb-Zn-based oxides, In-Lu-Zn-based oxides, and binary metal acids In-Zn oxides, Sn-Zn oxides, Al-Zn oxides, Zn-Mg oxides, Sn-Mg oxides, In-Mg oxides, In-Ga oxides The same applies to the case of using an oxide, an In-based oxide, a Sn-based oxide, a Zn-based oxide, or the like which is an oxide of a single metal.

For example, FIG. 20A illustrates a model diagram of a middle group that forms a layered structure of an In—Ga—Zn-based oxide.

In FIG. 20A, the middle group that forms the layer structure of the In—Ga—Zn-based oxide has four tetracoordinate O atoms in the upper half and the lower half in order from the top. Is bonded to Zn in the upper half, and through four tetracoordinate O atoms in the lower half of the Zn, Ga in which one tetracoordinate O atom is present in the upper half and the lower half one by one In this structure, three tetracoordinate O atoms are bonded to In in the upper half and the lower half through one tetracoordinate O atom in the lower half of the Ga. A plurality of medium groups are combined to form a large group.

FIG. 20B illustrates a large group including three medium groups. Note that FIG. 20C illustrates an atomic arrangement in the case where the layered structure in FIG. 20B is observed from the c-axis direction.

Here, charges of In (6-coordinate or 5-coordinate), Zn (4-coordinate), and Ga (5-coordinate) are +3, +2, and +3, respectively. The small group including the charge is 0. Therefore, in the case of a combination of these small groups, the total charge of the medium group is always zero.

Further, the middle group forming the layer structure of the In—Ga—Zn-based oxide is not limited to the middle group illustrated in FIG. 20A, and a large group in which middle groups having different arrangements of In, Ga, and Zn are combined. Groups can also be taken.

Specifically, the large group illustrated in FIG. 20B is repeated, whereby an In—Ga—Zn-based oxide crystal can be obtained. Note that the layered structure of the obtained In—Ga—Zn-based oxide can be represented by a composition formula, InGaO ₃ (ZnO) _n (n is a natural number).

In the case of n = 1 (InGaZnO ₄ ), for example, the crystal structure illustrated in FIG. Note that in the crystal structure illustrated in FIG. 21A, as described in FIG. 18B, since Ga and In have five coordination, a structure in which Ga is replaced with In can be used.

In the case of n = 2 (InGaZn ₂ O ₅ ), for example, the crystal structure shown in FIG. 21B can be taken. Note that in the crystal structure illustrated in FIG. 21B, as described in FIG. 18B, since Ga and In have five coordination, a structure in which Ga is replaced with In can be employed.

Next, as illustrated in FIG. 14A, a conductive film 719 in contact with the gate electrode 707 and in contact with the oxide semiconductor layer 716 and a conductive film 720 in contact with the conductive film 708 and in contact with the oxide semiconductor layer 716 are formed. Form. The conductive films 719 and 720 function as a source electrode or a drain electrode.

Specifically, the conductive film 719 and the conductive film 720 are formed by a sputtering method or a vacuum evaporation method so as to cover the gate electrode 707 and the conductive film 708, and then processed into a predetermined shape. Can be formed.

The conductive film to be the conductive film 719 and the conductive film 720 may be an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, tungsten, and magnesium, or an alloy containing any of the above elements as a component, or a combination of the above elements. Alloy films and the like. Alternatively, a high melting point metal film such as chromium, tantalum, titanium, molybdenum, or tungsten may be stacked below or above the metal film such as aluminum or copper. Aluminum or copper is preferably used in combination with a refractory metal material in order to avoid problems of heat resistance and corrosion. As the refractory metal material, molybdenum, titanium, chromium, tantalum, tungsten, neodymium, scandium, yttrium, or the like can be used.

The conductive film to be the conductive films 719 and 720 may have a single-layer structure or a stacked structure of two or more layers. For example, a single layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, a titanium film, an aluminum film laminated on the titanium film, and a titanium film formed on the titanium film. Examples include a three-layer structure. Further, Cu—Mg—Al alloy, Mo—Ti alloy, Ti, and Mo have high adhesion to the oxide film. Therefore, a conductive film composed of Cu—Mg—Al alloy, Mo—Ti alloy, Ti, or Mo is stacked in the lower layer, and a conductive film composed of Cu is stacked in the upper layer, and the stacked conductive film is used as the conductive film 719. By using the conductive film 720, the adhesion between the insulating film which is an oxide film and the conductive films 719 and 720 can be increased.

Alternatively, the conductive film to be the conductive films 719 and 720 may be formed using a conductive metal oxide. As the conductive metal oxide, indium oxide, tin oxide, zinc oxide, an indium tin oxide mixture, an indium zinc oxide mixture, or a metal oxide material containing silicon or silicon oxide can be used.

In the case where heat treatment is performed after formation of the conductive film, the conductive film preferably has heat resistance enough to withstand the heat treatment.

Note that each material and etching conditions are adjusted as appropriate so that the oxide semiconductor layer 716 is not removed as much as possible when the conductive film is etched. Depending on the etching conditions, a part of the exposed portion of the oxide semiconductor layer 716 may be etched to form a groove (a depressed portion).

In this embodiment, a titanium film is used for the conductive film. Therefore, the conductive film can be selectively wet-etched using a solution containing ammonia and aqueous hydrogen peroxide (ammonia hydrogen peroxide). Specifically, ammonia perwater obtained by mixing 31% by weight of hydrogen peroxide water, 28% by weight of ammonia water and water at a volume ratio of 5: 2: 2. Alternatively, the conductive film may be dry-etched using a gas containing chlorine (Cl ₂ ), boron chloride (BCl ₃ ), or the like.

Note that in order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that gives multi-level intensity to transmitted light. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

An oxide conductive film functioning as a source region and a drain region may be provided between the oxide semiconductor layer 716 and the conductive films 719 and 720 functioning as a source electrode and a drain electrode. As a material for the oxide conductive film, a material containing zinc oxide as a component is preferable, and a material not containing indium oxide is preferable. As such an oxide conductive film, zinc oxide, zinc aluminum oxide, zinc aluminum oxynitride, zinc gallium oxide, or the like can be used.

For example, in the case of forming an oxide conductive film, an etching process for forming the oxide conductive film and an etching process for forming the conductive film 719 and the conductive film 720 may be performed in a lump.

By providing the oxide conductive film functioning as the source region and the drain region, the resistance between the oxide semiconductor layer 716, the conductive film 719, and the conductive film 720 can be reduced; thus, high-speed operation of the transistor can be realized. it can. Further, by providing the oxide conductive film functioning as a source region and a drain region, the withstand voltage of the transistor can be increased.

Next, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar may be performed. Water or the like attached to the surface of the oxide semiconductor layer exposed by this plasma treatment is removed. Further, plasma treatment may be performed using a mixed gas of oxygen and argon.

Note that after the plasma treatment, a gate insulating film 721 is formed so as to cover the conductive films 719 and 720 and the oxide semiconductor layer 716 as illustrated in FIG. Then, a gate electrode 722 is formed over the gate insulating film 721 so as to overlap with the oxide semiconductor layer 716.

The gate insulating film 721 can be formed using a material similar to that of the gate insulating film 703 and a similar stacked structure. Note that the gate insulating film 721 preferably contains no impurities such as water and hydrogen as much as possible, and may be a single-layer insulating film or a plurality of stacked insulating films. When hydrogen is contained in the gate insulating film 721, the hydrogen penetrates into the oxide semiconductor layer 716, or the hydrogen extracts oxygen in the oxide semiconductor layer 716, so that the resistance of the oxide semiconductor layer 716 is reduced (n-type reduction). And a parasitic channel may be formed.

Therefore, it is important not to use hydrogen in the deposition method so that the gate insulating film 721 contains as little hydrogen as possible. The gate insulating film 721 preferably has an oxygen excess region. When the gate insulating film 721 has an oxygen-excess region, oxygen can be prevented from moving from the oxide semiconductor layer 716 to the gate insulating film 721 and from the gate insulating film 721 to the oxide semiconductor layer 716. This is because oxygen can be supplied.

Alternatively, the gate insulating film 721 may be formed using a material having a high barrier property against alkali metal or hydrogen and oxygen. Alternatively, the gate insulating film 721 may be a stack of an insulating film having an oxygen-excess region and an insulating film with high barrier properties. As the insulating film having a high barrier property, for example, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum oxide film, an aluminum oxynitride film, an aluminum nitride oxide film, or the like can be used. In the case where the gate insulating film 721 is a stack of an insulating film having an oxygen-excess region and an insulating film having a high barrier property, the insulating film having an oxygen-excess region may be formed in contact with the oxide semiconductor layer 716.

By using an insulating film having a high barrier property, impurities can be prevented from entering the oxide semiconductor layer 716 or the interface between the oxide semiconductor layer 716 and the insulating film and the vicinity thereof, and oxygen from the oxide semiconductor layer can be prevented. Desorption can be prevented.

In this embodiment, the gate insulating film 721 having a structure in which a silicon nitride film with a thickness of 100 nm formed by a sputtering method is stacked over a silicon oxide film with a thickness of 200 nm formed by a sputtering method is formed. . The substrate temperature at the time of film formation may be from room temperature to 300 ° C., and is 100 ° C. in this embodiment.

Note that heat treatment may be performed after the gate insulating film 721 is formed. The heat treatment is preferably performed at 200 ° C. to 400 ° C., for example, 250 ° C. to 350 ° C. in an atmosphere of nitrogen, ultra-dry air, or a rare gas (such as argon or helium). The gas preferably has a water content of 20 ppm or less, preferably 1 ppm or less, more preferably 10 ppb or less. In this embodiment, for example, heat treatment is performed at 250 ° C. for one hour in a nitrogen atmosphere. Alternatively, before the conductive films 719 and 720 are formed, high-temperature and short-time RTA treatment may be performed as in the previous heat treatment performed on the oxide semiconductor layer for reducing water or hydrogen. good. By the heat treatment performed after the gate insulating film 721 containing oxygen is provided, oxygen vacancies are generated in the oxide semiconductor layer 716 due to the previous heat treatment performed on the oxide semiconductor layer 716. Even so, oxygen is supplied from the gate insulating film 721 to the oxide semiconductor layer 716.

When oxygen is supplied to the oxide semiconductor layer 716, oxygen vacancies serving as donors in the oxide semiconductor layer 716 can be reduced and the stoichiometric composition ratio can be satisfied. As a result, the oxide semiconductor layer 716 can be made to be i-type, variation in electric characteristics of the transistor due to oxygen vacancies can be reduced, and electric characteristics can be improved. The timing of performing this heat treatment is not particularly limited as long as it is after the formation of the gate insulating film 721. Other processes, for example, heat treatment at the time of forming the resin film, and heat treatment for reducing the resistance of the transparent conductive film, By also serving, the oxide semiconductor layer 716 can be made to be i-type without increasing the number of steps.

Further, oxygen vacancies serving as donors in the oxide semiconductor layer 716 may be reduced by performing heat treatment on the oxide semiconductor layer 716 in an oxygen atmosphere so that oxygen is added to the oxide semiconductor. The temperature of the heat treatment is, for example, 100 ° C. or higher and lower than 350 ° C., preferably 150 ° C. or higher and lower than 250 ° C. The oxygen gas used for the heat treatment under the oxygen atmosphere preferably does not contain water, hydrogen, or the like. Alternatively, the purity of the oxygen gas introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration in oxygen is 1 ppm or less, preferably 0.1 ppm). Or less).

The gate electrode 722 can be formed by forming a conductive film over the gate insulating film 721 and etching the conductive film. The gate electrode 722 can be formed using a material similar to that of the gate electrode 707 or the conductive films 719 and 720.

The thickness of the gate electrode 722 is 10 nm to 400 nm, preferably 100 nm to 200 nm. In this embodiment, after a 150 nm gate electrode conductive film is formed by a sputtering method using a tungsten target, the conductive film is processed into a desired shape by etching, whereby the gate electrode 722 is formed. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Through the above process, the transistor 731 is formed.

Although the transistor 731 is described using a single-gate transistor, a multi-gate transistor having a plurality of channel formation regions by including a plurality of electrically connected gate electrodes as necessary can be used. Can be formed.

Note that for the insulating film in contact with the oxide semiconductor layer 716 (in this embodiment, the gate insulating film 721 corresponds), an insulating material containing a Group 13 element and oxygen may be used. Many oxide semiconductor materials contain a Group 13 element, and an insulating material containing a Group 13 element has good compatibility with an oxide semiconductor. By using this for an insulating film in contact with the oxide semiconductor layer, oxidation can be performed. The state of the interface with the physical semiconductor layer can be kept good.

An insulating material containing a Group 13 element means that the insulating material contains one or more Group 13 elements. Examples of the insulating material containing a Group 13 element include gallium oxide, aluminum oxide, aluminum gallium oxide, and gallium aluminum oxide. Here, aluminum gallium oxide indicates that the aluminum content (atomic%) is higher than gallium content (atomic%), and gallium aluminum oxide means that the gallium aluminum content (atomic%) contains aluminum. The amount (atomic%) or more is shown.

For example, when an insulating film is formed in contact with an oxide semiconductor layer containing gallium, the interface characteristics between the oxide semiconductor layer and the insulating film can be kept favorable by using a material containing gallium oxide for the insulating film. . For example, when an oxide semiconductor layer and an insulating film containing gallium oxide are provided in contact with each other, pileup of hydrogen at the interface between the oxide semiconductor layer and the insulating film can be reduced. Note that a similar effect can be obtained when an element of the same group as a constituent element of the oxide semiconductor is used for the insulating film. For example, it is also effective to form an insulating film using a material containing aluminum oxide. Note that aluminum oxide is a material having a barrier property and has a characteristic that water is difficult to permeate. Therefore, the use of the material is preferable in terms of preventing water from entering the oxide semiconductor layer.

Similarly to the gate insulating film 721, the insulating film 713 is preferably formed using a material having an oxygen-excess region (a region where oxygen is higher than the stoichiometric composition ratio). An insulating film having an oxygen-excess region may be formed between the insulating film 713 and the oxide semiconductor layer 716.

By performing oxygen doping treatment on the insulating film, an insulating film having an oxygen excess region can be obtained. Oxygen doping means adding oxygen to the bulk. The term “bulk” is used for the purpose of clarifying that oxygen is added not only to the surface of the thin film but also to the inside of the thin film. The oxygen dope includes oxygen plasma dope in which plasma oxygen is added to the bulk. Further, oxygen doping may be performed using an ion implantation method, an ion doping method, or a plasma doping method.

For example, in the case where gallium oxide is used as the insulating film in contact with the oxide semiconductor layer 716, the composition of gallium oxide is changed to Ga ₂ O _X (X = 3 + α, 0 <α by performing heat treatment in an oxygen atmosphere or oxygen doping. <1).

In the case where aluminum oxide is used as the insulating film in contact with the oxide semiconductor layer 716, the composition of the aluminum oxide is changed to Al ₂ O _X (X = 3 + α, 0 <α by performing heat treatment in an oxygen atmosphere or oxygen doping. <1).

In the case where gallium aluminum oxide (aluminum gallium oxide) is used as the insulating film in contact with the oxide semiconductor layer 716, the composition of gallium aluminum oxide (aluminum gallium oxide) is changed by performing heat treatment in an oxygen atmosphere or oxygen doping. _{Ga X Al 2-X O 3} + α (0 <X <2,0 <α <1) can be.

By forming an insulating film having an oxygen-excess region so as to be in contact with the oxide semiconductor layer 716 and performing heat treatment, excess oxygen in the insulating film is supplied to the oxide semiconductor layer. Alternatively, oxygen defects at the interface between the oxide semiconductor layer and the insulating film can be reduced, and the oxide semiconductor layer can be i-type or i-type as close as possible.

Note that the insulating film having an oxygen-excess region may be used for only one of the insulating film located in the upper layer or the insulating film located in the lower layer among the insulating films in contact with the oxide semiconductor layer 716. It is preferable to use it for both insulating films. By using an insulating film having an oxygen-excess region as an insulating film located above and below the insulating film in contact with the oxide semiconductor layer 716 and sandwiching the oxide semiconductor layer 716, the above effect can be further enhanced. Can do.

The insulating film used for the upper layer or the lower layer of the oxide semiconductor layer 716 may be an insulating film having the same constituent element in the upper layer and the lower layer, or may be an insulating film having different constituent elements. For example, the upper layer and the lower layer may be gallium oxide having a composition of Ga ₂ O _X (X = 3 + α, 0 <α <1), and one of the upper layer and the lower layer may have a composition of Ga ₂ O _X (X = 3 + α, 0 <Α <1) may be gallium oxide, and the other may be aluminum oxide having a composition of Al ₂ O _X (X = 3 + α, 0 <α <1).

The insulating film in contact with the oxide semiconductor layer 716 may be a stack of insulating films having an oxygen-excess region. For example, gallium oxide having a composition of Ga ₂ O _X (X = 3 + α, 0 <α <1) is formed over the oxide semiconductor layer 716, and the composition of the gallium oxide is Ga _X Al _{2 -X} O _{3 + α} (0 < You may form the gallium aluminum oxide (aluminum gallium oxide) of X <2, 0 <α <1).

Next, as illustrated in FIG. 14C, an insulating film 724 is formed so as to cover the gate insulating film 721 and the gate electrode 722. The insulating film 724 can be formed by a PVD method, a CVD method, or the like. Alternatively, the insulating layer can be formed using a material including an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, gallium oxide, or aluminum oxide. Note that the insulating film 724 is preferably formed using a material with a low dielectric constant or a structure with a low dielectric constant (such as a porous structure). This is because by reducing the dielectric constant of the insulating film 724, parasitic capacitance generated between wirings and electrodes can be reduced, and operation speed can be increased. Note that although the insulating film 724 has a single-layer structure in this embodiment, one embodiment of the present invention is not limited to this, and a stacked structure of two or more layers may be used.

Next, an opening 725 is formed in the gate insulating film 721 and the insulating film 724 so that part of the conductive film 720 is exposed. After that, a wiring 726 that is in contact with the conductive film 720 in the opening 725 is formed over the insulating film 724.

The wiring 726 is formed by forming a conductive film using a PVD method or a CVD method and then etching the conductive film. As a material for the conductive film, an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-described element as a component, or the like can be used. Any of manganese, magnesium, zirconium, beryllium, neodymium, scandium, or a combination of these materials may be used.

More specifically, for example, a method of forming an aluminum film so as to be embedded in the opening 725 after forming a thin titanium film (about 5 nm) by PVD in a region including the opening of the insulating film 724 can be used. . Here, the titanium film formed by the PVD method has a function of reducing an oxide film (natural oxide film or the like) on the surface to be formed and reducing contact resistance with the lower electrode or the like (here, the conductive film 720). Further, hillocks of the aluminum film can be prevented. Further, after forming a barrier film made of titanium, titanium nitride, or the like, a copper film may be formed by a plating method.

The opening 725 formed in the insulating film 724 is preferably formed in a region overlapping with the conductive film 708. By forming the opening 725 in such a region, an increase in element area due to the contact region can be suppressed.

Here, the case where the connection between the impurity region 704 and the conductive film 720 and the connection between the conductive film 720 and the wiring 726 are overlapped without using the conductive film 708 is described. In this case, an opening (referred to as a lower opening) is formed in the insulating film 712 and the insulating film 713 formed over the impurity region 704, a conductive film 720 is formed so as to cover the lower opening, and then the gate is formed. In the insulating film 721 and the insulating film 724, an opening (referred to as an upper opening) is formed in a region overlapping with the lower opening, and the wiring 726 is formed. When the upper opening is formed in a region overlapping with the lower opening, the conductive film 720 formed in the lower opening may be disconnected by etching. In order to avoid this, if the lower opening and the upper opening are formed so as not to overlap, there is a problem that the element area increases.

As shown in this embodiment mode, by using the conductive film 708, an upper opening can be formed without disconnecting the conductive film 720. Accordingly, since the lower opening and the upper opening can be provided so as to overlap with each other, an increase in element area due to the opening can be suppressed. That is, the degree of integration of the semiconductor device can be increased.

Next, an insulating film 727 is formed so as to cover the wiring 726. Through the series of steps described above, an FF circuit can be manufactured.

Note that in the above manufacturing method, the conductive films 719 and 720 functioning as a source electrode and a drain electrode are formed after the oxide semiconductor layer 716. Thus, as illustrated in FIG. 14B, in the transistor 731 obtained by the above manufacturing method, the conductive film 719 and the conductive film 720 are formed over the oxide semiconductor layer 716. However, in the transistor 731, a conductive film functioning as a source electrode and a drain electrode may be provided under the oxide semiconductor layer 716, that is, between the oxide semiconductor layer 716, the insulating film 712, and the insulating film 713. .

FIG. 15 is a cross-sectional view of the transistor 731 in the case where the conductive films 719 and 720 functioning as a source electrode and a drain electrode are provided between the oxide semiconductor layer 716, the insulating film 712, and the insulating film 713. Show. The transistor 731 illustrated in FIG. 15 can be obtained by forming the conductive film 719 and the conductive film 720 after forming the insulating film 713 and then forming the oxide semiconductor layer 716.

This embodiment can be implemented in combination with any of the above embodiments as appropriate.

(Embodiment 6)
In this embodiment, a transistor including an oxide semiconductor layer having a structure different from that in Embodiment 4 will be described with reference to a cross-sectional view in FIG. 16A to 16E illustrate structural examples of top-gate transistors. FIGS. 16A, 16C, and 16E show structural examples of planar (coplanar) transistors, and FIGS. 16B and 16D show staggered transistors. The structure example of a type transistor is shown.

A transistor 901 illustrated in FIG. 16A includes an oxide semiconductor layer 903 that functions as an active layer and is formed over a base film 902, and a source electrode 904 and a drain electrode 905 that are formed over the oxide semiconductor layer 903. A gate insulating film 906 over the oxide semiconductor layer 903, the source electrode 904, and the drain electrode 905, a gate electrode 907 provided on the gate insulating film 906 so as to overlap with the oxide semiconductor layer 903, and over the gate electrode 907 A protective insulating film 910 which covers the oxide semiconductor layer 903.

A transistor 901 illustrated in FIG. 16A is a top-gate transistor in which a gate electrode 907 is formed over an oxide semiconductor layer 903, and a source electrode 904 and a drain electrode 905 are formed over the oxide semiconductor layer 903. The top contact type formed in In the transistor 901, the source electrode 904 and the drain electrode 905 are not overlapped with the gate electrode 907. That is, a gap larger than the thickness of the gate insulating film 906 is provided between the source electrode 904 and the drain electrode 905 and the gate electrode 907. Accordingly, the transistor 901 can suppress a parasitic capacitance formed between the source electrode 904 and the drain electrode 905 and the gate electrode 907, so that high-speed operation can be realized.

The oxide semiconductor layer 903 includes a pair of high-concentration regions 908 obtained by adding a dopant that imparts n-type conductivity to the oxide semiconductor layer 903 after the gate electrode 907 is formed. Further, in the oxide semiconductor layer 903, a region which overlaps with the gate electrode 907 with the gate insulating film 906 interposed therebetween is a channel formation region 909. In the oxide semiconductor layer 903, a channel formation region 909 is provided between the pair of high concentration regions 908. The dopant for forming the high concentration region 908 can be added by an ion implantation method. As the dopant, for example, a rare gas such as helium, argon, or xenon, nitrogen, phosphorus, arsenic, antimony, boron, or the like can be used.

For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the high concentration region 908 is preferably 5 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²² / cm ³ or less.

The high-concentration region 908 to which a dopant imparting n-type conductivity is added has higher conductivity than other regions in the oxide semiconductor layer 903. Therefore, the resistance between the source electrode 904 and the drain electrode 905 can be reduced by providing the high-concentration region 908 in the oxide semiconductor layer 903.

In the case where an In—Ga—Zn-based oxide is used for the oxide semiconductor layer 903, heat treatment is performed at a temperature of 300 ° C. to 600 ° C. for about 1 hour after adding nitrogen. An oxide semiconductor has a wurtzite crystal structure. When the oxide semiconductor in the high concentration region 908 has a wurtzite crystal structure, the conductivity of the high concentration region 908 can be further increased and the resistance between the source electrode 904 and the drain electrode 905 can be reduced. Note that in order to form an oxide semiconductor having a wurtzite crystal structure and effectively reduce the resistance between the source electrode 904 and the drain electrode 905, when nitrogen is used as a dopant, the high concentration region 908 is used. It is desirable that the concentration of nitrogen atoms in the inside be 1 × 10 ²⁰ / cm ³ or more and 7 atoms% or less. However, an oxide semiconductor having a wurtzite crystal structure may be obtained even when the concentration of nitrogen atoms is lower than the above range.

The oxide semiconductor layer 903 may be formed using a CAAC-OS. In the case where the oxide semiconductor layer 903 is formed using a CAAC-OS, the conductivity of the oxide semiconductor layer 903 can be increased as compared with the case where the oxide semiconductor layer 903 is amorphous, and thus the resistance between the source electrode 904 and the drain electrode 905 is increased. Can be lowered.

By reducing the resistance between the source electrode 904 and the drain electrode 905, high on-state current and high-speed operation can be ensured even when the transistor 901 is miniaturized. Further, by miniaturization of the transistor 901, the area occupied by a semiconductor device using the transistor can be reduced and the number of transistors per unit area can be increased.

A transistor 911 illustrated in FIG. 16B includes a source electrode 914 and a drain electrode 915 formed over a base film 912, and an oxide semiconductor layer 913 functioning as an active layer formed over the source electrode 914 and the drain electrode 915. A gate insulating film 916 over the oxide semiconductor layer 913, the source electrode 914, and the drain electrode 915, a gate electrode 917 provided on the gate insulating film 916 so as to overlap with the oxide semiconductor layer 913, and a gate electrode 917 A protective insulating film 920 covering the oxide semiconductor layer 913.

A transistor 911 illustrated in FIG. 16B is a top-gate transistor in which a gate electrode 917 is formed over an oxide semiconductor layer 913, and a source electrode 914 and a drain electrode 915 are formed under the oxide semiconductor layer 913. The bottom contact type formed in Since the source electrode 914 and the drain electrode 915 do not overlap with the gate electrode 917 as in the transistor 901, the transistor 911 is a parasitic formed between the source electrode 914 and the drain electrode 915 and the gate electrode 917. The capacity can be kept small, and high-speed operation can be realized.

The oxide semiconductor layer 913 includes a pair of high-concentration regions 918 obtained by adding a dopant that imparts n-type conductivity to the oxide semiconductor layer 913 after the gate electrode 917 is formed. In the oxide semiconductor layer 913, a region overlapping with the gate electrode 917 with the gate insulating film 916 interposed therebetween is a channel formation region 919. In the oxide semiconductor layer 913, a channel formation region 919 is provided between the pair of high concentration regions 918.

The high concentration region 918 can be formed by an ion implantation method as in the case of the high concentration region 908 included in the transistor 901 described above. For the type of dopant for forming the high concentration region 918, the case of the high concentration region 908 can be referred to.

For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the high concentration region 918 is preferably 5 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²² / cm ³ or less.

The high-concentration region 918 to which the dopant imparting n-type conductivity is added has higher conductivity than other regions in the oxide semiconductor layer 913. Therefore, by providing the high-concentration region 918 in the oxide semiconductor layer 913, resistance between the source electrode 914 and the drain electrode 915 can be reduced.

In the case where an In—Ga—Zn-based oxide is used for the oxide semiconductor layer 913, the oxide in the high-concentration region 918 is subjected to heat treatment at about 300 ° C. to 600 ° C. after adding nitrogen. The semiconductor has a wurtzite crystal structure. When the oxide semiconductor in the high concentration region 918 has a wurtzite crystal structure, the conductivity of the high concentration region 918 can be further increased and the resistance between the source electrode 914 and the drain electrode 915 can be reduced. Note that in order to form an oxide semiconductor having a wurtzite crystal structure and effectively reduce the resistance between the source electrode 914 and the drain electrode 915, when nitrogen is used as a dopant, the high concentration region 918 is used. It is desirable that the concentration of nitrogen atoms in the inside be 1 × 10 ²⁰ / cm ³ or more and 7 atoms% or less. However, an oxide semiconductor having a wurtzite crystal structure may be obtained even when the concentration of nitrogen atoms is lower than the above range.

The oxide semiconductor layer 913 may be formed using a CAAC-OS. In the case where the oxide semiconductor layer 913 is formed using a CAAC-OS, the conductivity of the oxide semiconductor layer 913 can be higher than that in the case where the oxide semiconductor layer 913 is amorphous; thus, the resistance between the source electrode 914 and the drain electrode 915 can be increased. Can be lowered.

Then, by reducing the resistance between the source electrode 914 and the drain electrode 915, high on-state current and high-speed operation can be ensured even when the transistor 911 is miniaturized. Further, by miniaturization of the transistor 911, an area occupied by a semiconductor device using the transistor can be reduced and the number of transistors per unit area can be increased.

A transistor 921 illustrated in FIG. 16C includes an oxide semiconductor layer 923 that functions as an active layer formed over a base film 922, a source electrode 924, and a drain electrode 925 formed over the oxide semiconductor layer 923. A gate insulating film 926 over the oxide semiconductor layer 923, the source electrode 924, and the drain electrode 925, a gate electrode 927 provided on the gate insulating film 926 so as to overlap with the oxide semiconductor layer 923, and over the gate electrode 927 A protective insulating film 932 covering the oxide semiconductor layer 923; Further, the transistor 921 includes a sidewall 930 formed of an insulator and provided on a side portion of the gate electrode 927.

A transistor 921 illustrated in FIG. 16C is a top-gate transistor in which a gate electrode 927 is formed over the oxide semiconductor layer 923, and a source electrode 924 and a drain electrode 925 are formed over the oxide semiconductor layer 923. The top contact type formed in Since the source electrode 924, the drain electrode 925, and the gate electrode 927 do not overlap with each other as in the transistor 901, the transistor 921 is a parasitic element formed between the source electrode 924, the drain electrode 925, and the gate electrode 927. The capacity can be kept small, and high-speed operation can be realized.

The oxide semiconductor layer 923 includes a pair of high-concentration regions 928 obtained by adding a dopant imparting n-type conductivity to the oxide semiconductor layer 923 after the gate electrode 927 is formed, and a pair of And a low concentration region 929. In the oxide semiconductor layer 923, a region overlapping with the gate electrode 927 with the gate insulating film 926 interposed therebetween is a channel formation region 931. In the oxide semiconductor layer 923, a pair of low concentration regions 929 is provided between the pair of high concentration regions 928, and a channel formation region 931 is provided between the pair of low concentration regions 929. The pair of low-concentration regions 929 are provided in regions of the oxide semiconductor layer 923 that overlap with the sidewalls 930 with the gate insulating film 926 interposed therebetween.

The high concentration region 928 and the low concentration region 929 can be formed by an ion implantation method as in the case of the high concentration region 908 included in the transistor 901 described above. For the type of dopant for forming the high concentration region 928, the case of the high concentration region 908 can be referred to.

For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the high concentration region 928 is preferably 5 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²² / cm ³ or less. For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the low-concentration region 929 is preferably 5 × 10 ¹⁸ / cm ³ or more and less than 5 × 10 ¹⁹ / cm ³ .

The high-concentration region 928 to which the dopant imparting n-type conductivity is added has higher conductivity than the other regions in the oxide semiconductor layer 923. Therefore, the resistance between the source electrode 924 and the drain electrode 925 can be reduced by providing the high-concentration region 928 in the oxide semiconductor layer 923. Further, by providing the low concentration region 929 between the channel formation region 931 and the high concentration region 928, a minus shift of the threshold voltage due to the short channel effect can be reduced.

In the case where an In—Ga—Zn-based oxide is used for the oxide semiconductor layer 923, the oxide in the high concentration region 928 is subjected to heat treatment at about 300 ° C. to 600 ° C. after adding nitrogen. The semiconductor has a wurtzite crystal structure. Furthermore, the low concentration region 929 may also have a wurtzite crystal structure by the above heat treatment depending on the concentration of nitrogen. When the oxide semiconductor in the high concentration region 928 has a wurtzite crystal structure, the conductivity of the high concentration region 928 can be further increased and the resistance between the source electrode 924 and the drain electrode 925 can be decreased. Note that in order to form an oxide semiconductor having a wurtzite crystal structure and effectively reduce the resistance between the source electrode 924 and the drain electrode 925, when nitrogen is used as a dopant, the high concentration region 928 is used. It is desirable that the concentration of nitrogen atoms in the inside be 1 × 10 ²⁰ / cm ³ or more and 7 atoms% or less. However, an oxide semiconductor having a wurtzite crystal structure may be obtained even when the concentration of nitrogen atoms is lower than the above range.

The oxide semiconductor layer 923 may be formed using a CAAC-OS. In the case where the oxide semiconductor layer 923 is formed using a CAAC-OS, the conductivity of the oxide semiconductor layer 923 can be higher than that in the case where the oxide semiconductor layer 923 is amorphous; thus, the resistance between the source electrode 924 and the drain electrode 925 can be increased. Can be lowered.

Further, by reducing the resistance between the source electrode 924 and the drain electrode 925, high on-state current and high-speed operation can be ensured even when the transistor 921 is miniaturized. Further, by miniaturization of the transistor 921, an area occupied by a semiconductor device including the transistor can be reduced and the number of transistors per unit area can be increased.

A transistor 941 illustrated in FIG. 16D includes a source electrode 944 and a drain electrode 945 formed over a base film 942, and an oxide semiconductor layer 943 functioning as an active layer formed over the source electrode 944 and the drain electrode 945. A gate insulating film 946 over the oxide semiconductor layer 943, the source electrode 944, and the drain electrode 945, a gate electrode 947 provided on the gate insulating film 946 so as to overlap with the oxide semiconductor layer 943, and the gate electrode 947 The protective insulating film 952 which covers the oxide semiconductor layer 943 is provided. Further, the transistor 941 includes a sidewall 950 that is provided on a side portion of the gate electrode 947 and is formed using an insulator.

A transistor 941 illustrated in FIG. 16D is a top-gate transistor in which a gate electrode 947 is formed over the oxide semiconductor layer 943, and a source electrode 944 and a drain electrode 945 are formed under the oxide semiconductor layer 943. The bottom contact type formed in Since the source electrode 944 and the drain electrode 945 do not overlap with the gate electrode 947, the transistor 941 is a parasitic element formed between the source electrode 944 and the drain electrode 945 and the gate electrode 947, as in the transistor 901. The capacity can be kept small, and high-speed operation can be realized.

The oxide semiconductor layer 943 includes a pair of high-concentration regions 948 and a pair of high-concentration regions 948 obtained by adding a dopant that imparts n-type conductivity to the oxide semiconductor layer 943 after the gate electrode 947 is formed. And a low concentration region 949. Further, in the oxide semiconductor layer 943, a region overlapping with the gate electrode 947 with the gate insulating film 946 interposed therebetween is a channel formation region 951. In the oxide semiconductor layer 943, a pair of low concentration regions 949 is provided between the pair of high concentration regions 948, and a channel formation region 951 is provided between the pair of low concentration regions 949. The pair of low-concentration regions 949 are provided in regions of the oxide semiconductor layer 943 that overlap with the sidewalls 950 with the gate insulating film 946 interposed therebetween.

The high concentration region 948 and the low concentration region 949 can be formed by an ion implantation method as in the case of the high concentration region 908 included in the transistor 901 described above. For the type of dopant for forming the high concentration region 948, the case of the high concentration region 908 can be referred to.

For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the high concentration region 948 is preferably 5 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²² / cm ³ or less. For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the low concentration region 949 is desirably 5 × 10 ¹⁸ / cm ³ or more and less than 5 × 10 ¹⁹ / cm ³ .

The high-concentration region 948 to which the dopant imparting n-type conductivity is added has higher conductivity than the other regions in the oxide semiconductor layer 943. Therefore, by providing the high-concentration region 948 in the oxide semiconductor layer 943, the resistance between the source electrode 944 and the drain electrode 945 can be reduced. Further, by providing the low concentration region 949 between the channel formation region 951 and the high concentration region 948, a minus shift of the threshold voltage due to the short channel effect can be reduced.

In the case where an In—Ga—Zn-based oxide is used for the oxide semiconductor layer 943, the oxide in the high-concentration region 948 is subjected to heat treatment at about 300 ° C. to 600 ° C. after adding nitrogen. The semiconductor has a wurtzite crystal structure. Furthermore, the low concentration region 949 may have a wurtzite crystal structure by the above heat treatment depending on the concentration of nitrogen. When the oxide semiconductor in the high concentration region 948 has a wurtzite crystal structure, the conductivity of the high concentration region 948 can be further increased and the resistance between the source electrode 944 and the drain electrode 945 can be reduced. Note that in order to form an oxide semiconductor having a wurtzite crystal structure and effectively reduce the resistance between the source electrode 944 and the drain electrode 945, when nitrogen is used as a dopant, the high concentration region 948 is used. It is desirable that the concentration of nitrogen atoms in the inside be 1 × 10 ²⁰ / cm ³ or more and 7 atoms% or less. However, an oxide semiconductor having a wurtzite crystal structure may be obtained even when the concentration of nitrogen atoms is lower than the above range.

The oxide semiconductor layer 943 may be formed using a CAAC-OS. In the case where the oxide semiconductor layer 943 is formed using a CAAC-OS, the conductivity of the oxide semiconductor layer 943 can be higher than that in the case where the oxide semiconductor layer 943 is amorphous; thus, the resistance between the source electrode 944 and the drain electrode 945 can be increased. Can be lowered.

By reducing the resistance between the source electrode 944 and the drain electrode 945, high on-state current and high-speed operation can be ensured even when the transistor 941 is miniaturized. Further, by miniaturization of the transistor 941, an area occupied by a semiconductor device using the transistor can be reduced and the number of transistors per unit area can be increased.

A transistor 961 illustrated in FIG. 16E includes an oxide semiconductor layer 963 that functions as an active layer, which is formed over a base film 962, and a source electrode 964 and a drain electrode 965 that are formed over the oxide semiconductor layer 963. The gate electrode 967 provided on the gate insulating film 966 so as to overlap with the oxide semiconductor layer 963, the side wall 970 formed of an insulator provided on the side of the gate electrode 967, and the gate electrode 967 A protective insulating film 972 covering the oxide semiconductor layer 963 and an insulating film 973 over the protective insulating film 972 are provided. Further, the transistor 961 includes a protective insulating film 972, an electrode 974 that is electrically connected to the source electrode 964 through a contact hole provided in the insulating film 973, and an electrode 975 that is electrically connected to the drain electrode 965.

The insulating film 973 can be formed using a material including an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide. Alternatively, it can be formed using an organic insulating material such as polyimide or acrylic.

In addition, after the insulating film 973 is formed, it is preferable to perform planarization treatment for reducing a step on the surface of the insulating film 973 by CMP treatment, etching treatment, or the like. By reducing the level difference on the surface of the insulating film 973, coverage with electrodes and wirings formed in a later step can be improved, and high integration of the semiconductor device is facilitated. Furthermore, since it is difficult for the wiring resistance to increase at the step over the step and the disconnection of the wiring due to poor coverage, the reliability of the semiconductor device can be improved.

The transistor 961 is a top gate type in which a gate electrode 967 is formed over the oxide semiconductor layer 963, and a top contact in which a source electrode 964 and a drain electrode 965 are formed over the oxide semiconductor layer 963. It is a type. The transistor 961 is formed between the source electrode 964 and the drain electrode 965 and the gate electrode 967 because the source electrode 964 and the drain electrode 965 do not overlap with the gate electrode 967, as in the transistor 901. Parasitic capacitance can be reduced and high-speed operation can be realized.

The oxide semiconductor layer 963 includes a pair of high-concentration regions 968 obtained by adding a dopant imparting n-type conductivity to the oxide semiconductor layer 963 after the gate electrode 967 is formed, and a pair of And a low concentration region 969. In the oxide semiconductor layer 963, a region overlapping with the gate electrode 967 with the gate insulating film 966 interposed therebetween is a channel formation region 971. In the oxide semiconductor layer 963, a pair of low concentration regions 969 is provided between the pair of high concentration regions 968, and a channel formation region 971 is provided between the pair of low concentration regions 969. The pair of low-concentration regions 969 are provided in regions of the oxide semiconductor layer 963 that overlap with the sidewalls 970 with the gate insulating film 966 interposed therebetween.

The high concentration region 968 and the low concentration region 969 can be formed by an ion implantation method as in the case of the high concentration region 908 included in the transistor 901 described above. For the type of dopant for forming the high concentration region 968, the case of the high concentration region 908 can be referred to.

For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the high concentration region 968 is preferably 5 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²² / cm ³ or less. For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the low-concentration region 969 is preferably 5 × 10 ¹⁸ / cm ³ or more and less than 5 × 10 ¹⁹ / cm ³ .

The high-concentration region 968 to which the dopant imparting n-type conductivity is added has higher conductivity than other regions in the oxide semiconductor layer 963. Therefore, by providing the high-concentration region 968 in the oxide semiconductor layer 963, the resistance between the source electrode 964 and the drain electrode 965 can be reduced. Further, by providing the low concentration region 969 between the channel formation region 971 and the high concentration region 968, a minus shift of the threshold voltage due to the short channel effect can be reduced.

In the case where an In—Ga—Zn-based oxide is used for the oxide semiconductor layer 963, after adding nitrogen, heat treatment is performed at about 300 ° C. to 600 ° C., whereby the oxide in the high-concentration region 968 is obtained. The semiconductor has a wurtzite crystal structure. Further, the low concentration region 969 may have a wurtzite crystal structure by the above heat treatment depending on the concentration of nitrogen. When the oxide semiconductor in the high concentration region 968 has a wurtzite crystal structure, the conductivity of the high concentration region 968 can be further increased and the resistance between the source electrode 964 and the drain electrode 965 can be reduced. Note that in order to form an oxide semiconductor having a wurtzite crystal structure and effectively reduce the resistance between the source electrode 964 and the drain electrode 965, when nitrogen is used as a dopant, the high-concentration region 968 is used. It is desirable that the concentration of nitrogen atoms in the inside be 1 × 10 ²⁰ / cm ³ or more and 7 atoms% or less. However, an oxide semiconductor having a wurtzite crystal structure may be obtained even when the concentration of nitrogen atoms is lower than the above range.

The oxide semiconductor layer 963 may be formed using a CAAC-OS. In the case where the oxide semiconductor layer 963 is formed using a CAAC-OS, the conductivity of the oxide semiconductor layer 963 can be higher than that in the case where the oxide semiconductor layer 963 is amorphous. Therefore, the resistance between the source electrode 964 and the drain electrode 965 is increased. Can be lowered.

Then, by reducing the resistance between the source electrode 964 and the drain electrode 965, high on-state current and high-speed operation can be ensured even when the transistor 961 is miniaturized. Further, by miniaturization of the transistor 961, the area occupied by a semiconductor device using the transistor can be reduced and the number of transistors per unit area can be increased.

Note that in a transistor including an oxide semiconductor, as one method for manufacturing a high-concentration region functioning as a source region or a drain region by a self-alignment process, the surface of the oxide semiconductor layer is exposed and argon plasma treatment is performed. And the method of reducing the resistivity of the oxide semiconductor layer exposed to plasma has been disclosed (S. Jeon et al. “180 nm Gate Length Amorphous InGaZnO Thin Film Transistor for High Density Image Sensitive Image Amplification”). IEDM Tech.Dig., Pp.504-507, 2010.).

However, in the above manufacturing method, after forming the gate insulating film, it is necessary to partially remove the gate insulating film so as to expose a portion to be a source region or a drain region. Therefore, when the gate insulating film is removed, the lower oxide semiconductor layer is also partially over-etched, and the thickness of a portion to be a source region or a drain region is reduced. As a result, the resistance of the source region or the drain region is increased, and the transistor characteristics are likely to be deteriorated due to over-etching.

In order to advance the miniaturization of transistors, it is necessary to employ a dry etching method with high processing accuracy. However, the overetching is remarkably likely to occur when a dry etching method is employed in which a sufficient selection ratio between the oxide semiconductor layer and the gate insulating film cannot be ensured.

For example, overetching is not a problem when the oxide semiconductor layer has a sufficient thickness. However, when the channel length is set to 200 nm or less, in order to prevent the short channel effect, The thickness of the oxide semiconductor layer is required to be 20 nm or less, preferably 10 nm or less. In the case of handling such a thin oxide semiconductor layer, overetching of the oxide semiconductor layer is not preferable because the resistance of the source region or the drain region as described above is increased and the characteristics of the transistor are deteriorated.

However, as in one embodiment of the present invention, overetching of the oxide semiconductor layer is performed by adding the dopant to the oxide semiconductor layer without exposing the oxide semiconductor layer and leaving the gate insulating film. And excessive damage to the oxide semiconductor layer can be reduced. In addition, the interface between the oxide semiconductor layer and the gate insulating film is kept clean. Accordingly, the characteristics and reliability of the transistor can be improved.

For the base film and the protective insulating film located below the oxide semiconductor layer, it is preferable to use a material having a high barrier property against alkali metal, hydrogen, and oxygen. For example, as the insulating film with high barrier properties, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum oxide film, an aluminum oxynitride film, an aluminum nitride oxide film, or the like can be used. The base film and the protective insulating film may be a single layer or a stack of insulating films with high barrier properties, or a stack of an insulating film with high barrier properties and an insulating film with low barrier properties.

By covering the oxide semiconductor layer with an insulating film having a high barrier property, intrusion of impurities from the outside can be prevented and oxygen desorption from the oxide semiconductor layer can be prevented. Thus, the reliability of the transistor can be improved.

This embodiment can be implemented in combination with any of the above embodiments as appropriate.

(Embodiment 7)
With the use of the divider circuit according to one embodiment of the present invention, an electronic device with high reliability and an electronic device with reduced power consumption can be provided. In particular, in the case of a portable electronic device that is difficult to receive power supply at all times, the use of a frequency dividing circuit with low power consumption according to one embodiment of the present invention as a component increases the continuous use time. Benefits are gained.

A divider circuit according to one embodiment of the present invention can reproduce a display device, a personal computer, an image reproduction device including a recording medium (typically, a recording medium such as a DVD: Digital Versatile Disc, and display the image) It can be used for a device having a display. In addition, as an electronic device that can use the divider circuit according to one embodiment of the present invention, a mobile phone, a game machine including a portable type, a portable information terminal, an electronic book, a video camera, a digital still camera, a goggle type display ( Head mounted display), navigation system, sound reproduction device (car audio, digital audio player, etc.), copying machine, facsimile, printer, printer multifunction device, automatic teller machine (ATM), vending machine, and the like. Specific examples of these electronic devices are shown in FIGS.

FIG. 17A illustrates an e-book reader which includes a housing 7001, a display portion 7002, and the like. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the electronic book. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the electronic book, an electronic book with reduced power consumption can be provided. In addition, since an integrated circuit can have flexibility by using a flexible substrate, an electronic book that is flexible, light, and easy to use can be provided.

FIG. 17B illustrates a display device, which includes a housing 7011, a display portion 7012, a support base 7013, and the like. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the display device. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the display device, a display device with reduced power consumption can be provided. The display device includes all information display devices for personal computers, TV broadcast reception, advertisement display, and the like.

FIG. 17C illustrates a display device, which includes a housing 7021, a display portion 7022, and the like. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the display device. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the display device, a display device with reduced power consumption can be provided. In addition, since the integrated circuit can be flexible by using a flexible substrate, a flexible, light, and easy-to-use display device can be provided. Accordingly, as illustrated in FIG. 17C, the display device can be used by being fixed to a cloth or the like, and the range of application of the display device is significantly widened.

FIG. 17D illustrates a portable game machine including a housing 7031, a housing 7032, a display portion 7033, a display portion 7034, a microphone 7035, speakers 7036, operation keys 7037, a stylus 7038, and the like. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the portable game machine. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the portable game machine, a portable game machine with reduced power consumption can be provided. Note that although the portable game machine illustrated in FIG. 17D includes two display portions 7033 and 7034, the number of display portions included in the portable game device is not limited thereto.

FIG. 17E illustrates a mobile phone, which includes a housing 7041, a display portion 7042, an audio input portion 7043, an audio output portion 7044, operation keys 7045, a light receiving portion 7046, and the like. An external image can be captured by converting the light received by the light receiving unit 7046 into an electrical signal. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the mobile phone. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the mobile phone, a mobile phone with reduced power consumption can be provided.

FIG. 17F illustrates a portable information terminal which includes a housing 7051, a display portion 7052, operation keys 7053, and the like. In the portable information terminal illustrated in FIG. 17F, a modem may be incorporated in the housing 7051. The divider circuit according to one embodiment of the present invention can be used for an integrated circuit for controlling driving of the portable information terminal. By using the divider circuit according to one embodiment of the present invention for the integrated circuit for controlling driving of the portable information terminal, a portable information terminal with reduced power consumption can be provided.

This embodiment can be implemented in combination with any of the above embodiments as appropriate.

In this example, field effect mobility of a transistor using an ideal oxide semiconductor in which a semiconductor layer in which a channel is formed is free from defects inside the semiconductor will be described.

The field-effect mobility of an insulated gate transistor that is actually measured, not limited to an oxide semiconductor, is lower than the original mobility for various reasons. Factors that decrease the mobility include defects inside the semiconductor and defects at the interface between the semiconductor and the insulating film. However, using the Levinson model, the field-effect mobility is theoretically assumed when there is no defect inside the semiconductor. Can be derived.

Assuming that the intrinsic mobility (Hall mobility) of the semiconductor is μ ₀ , the measured field effect mobility is μ, and that some potential barrier (grain boundary or the like) exists in the semiconductor, it can be expressed by the following equation.

Here, E is the height of the potential barrier, k is the Boltzmann constant, and T is the absolute temperature. Assuming that the potential barrier is derived from defects, the Levinson model is represented by the following equation.

Here, e is the elementary charge, N is the average defect density per unit area in the channel, ε is the dielectric constant of the semiconductor, n is the number of carriers contained in the channel per unit area, and C _ox is the capacity per unit area , V _g is the gate voltage, and t is the channel thickness. Note that in the case of a semiconductor layer having a thickness of 30 nm or less, the thickness of the channel may be the same as the thickness of the semiconductor layer.
The drain current I _d in the linear region is expressed by the following equation.

Here, L is the channel length, and W is the channel width. Here, L = W = 10 μm. V _d is the drain voltage.
Dividing both sides of the above equation by V _g and taking the logarithm of both sides gives the following.

Number 4 of the right-hand side is a function of V _g. As seen from this equation, the vertical axis the _{ln (I d / V g)} , the horizontal axis 1 / V _g as a defect density N from the slope of the straight line of the graph obtained by plotting the measured values is obtained. That is, the defect density can be evaluated from the I _d -V _g characteristics of the transistor. As an oxide semiconductor, when the ratio of indium (In), tin (Sn), and zinc (Zn) is In: Sn: Zn = 1: 1: 1, the defect density N is about 1 × 10 ¹² / cm ^2. It is.

Μ ₀ = 120 cm ² / Vs is derived from Equation 1 and Equation ² based on the defect density and the like thus obtained. The mobility measured with a defective In—Sn—Zn oxide is about 35 cm ² / Vs. However, it can be expected that the mobility μ ₀ of an oxide semiconductor having no defects inside the semiconductor and at the interface between the semiconductor and the insulating film is 120 cm ² / Vs.

However, even if there is no defect inside the semiconductor, the transport characteristics of the transistor are affected by scattering at the interface between the channel and the gate insulating film. That is, the field effect mobility μ _{1 at} a location separated by x from the gate insulating film interface is expressed by the following equation.

Here, D is an electric field in the gate direction, and B and G are constants. B and G can be obtained from actual measurement results. From the above measurement results, B = 4.75 × 10 ⁷ cm / s and G = 10 nm (depth at which interface scattering reaches). It can be seen that as D increases (that is, the gate voltage increases), the second term of Formula 5 increases, and thus the field-effect mobility μ ₁ decreases.

FIG. 22 shows the result of calculating the field-effect mobility μ ₂ of a transistor using an ideal oxide semiconductor having no defects inside the semiconductor as a channel. For the calculation, device simulation software manufactured by Synopsys, Sentaurus Device was used, and the band gap, electron affinity, relative permittivity, and thickness of the oxide semiconductor were 2.8 eV, 4.7 eV, and 15 respectively. 15 nm. These values are obtained by measuring a thin film formed by a sputtering method.

Furthermore, the work functions of the gate, source, and drain were set to 5.5 eV, 4.6 eV, and 4.6 eV, respectively. The thickness of the gate insulating film was 100 nm and the relative dielectric constant was 4.1. Channel length and the channel width were each 10 [mu] m, the drain voltage _{V d} is 0.1 V.

As shown in FIG. 22, a peak of a mobility of 100 cm ² / Vs or higher is obtained at a gate voltage of slightly higher than 1 V. However, when the gate voltage is further increased, interface scattering increases and the mobility decreases. In order to reduce interface scattering, it is desirable to flatten the surface of the semiconductor layer at the atomic level (Atomic Layer Flatness).

Results of calculation of characteristics in the case where a minute transistor is manufactured using an oxide semiconductor having such mobility are illustrated in FIGS. Note that FIG. 26 illustrates a cross-sectional structure of the transistor used for the calculation. The transistor illustrated in FIGS. 26A and 26B includes a semiconductor region 1103a and a semiconductor region 1103c exhibiting an n ⁺ conductivity type in an oxide semiconductor layer. The resistivity of the semiconductor region 1103a and the semiconductor region 1103c is 2 × 10 ⁻³ Ωcm.

The transistor illustrated in FIG. 26A is formed over a base insulating layer 1101 and a buried insulator 1102 formed of aluminum oxide so as to be embedded in the base insulating layer 1101. The transistor includes a semiconductor region 1103a, a semiconductor region 1103c, an intrinsic semiconductor region 1103b which is sandwiched therebetween and serves as a channel formation region, and a gate 1105. The width of the gate 1105 is 33 nm.

A gate insulating film 1104 is provided between the gate 1105 and the semiconductor region 1103b. Side wall insulators 1106a and 1106b are formed on both sides of the gate 1105, and the gate 1105 and other regions are formed on the gate 1105. An insulator 1107 is provided for preventing a short circuit with the wiring. The width of the sidewall insulator is 5 nm. In addition, the semiconductor region 1103a and the semiconductor region 1103c are in contact with the source 1108a and the drain 1108b. Note that the channel width of this transistor is 40 nm.

The transistor illustrated in FIG. 26B is formed over a base insulating layer 1101, a buried insulator 1102 made of aluminum oxide, a semiconductor region 1103a, a semiconductor region 1103c, and an intrinsic semiconductor region 1103b sandwiched between them. The transistor is the same as the transistor illustrated in FIG. 26A in that it includes a gate 1105 having a width of 33 nm, a gate insulating film 1104, a sidewall insulator 1106a, a sidewall insulator 1106b, an insulator 1107, a source 1108a, and a drain 1108b.

A difference between the transistor illustrated in FIG. 26A and the transistor illustrated in FIG. 26B is the conductivity type of the semiconductor region under the sidewall insulator 1106a and the sidewall insulator 1106b. In the transistor illustrated in FIG. 26A, the semiconductor regions under the sidewall insulator 1106a and the sidewall insulator 1106b are the semiconductor region 1103a and the semiconductor region 1103c having n ⁺ conductivity type, but are illustrated in FIG. In the transistor, the intrinsic semiconductor region 1103b. That is, in the semiconductor layer illustrated in FIG. 26B, a region where the semiconductor region 1103a (semiconductor region 1103c) and the gate 1105 do not overlap with each other by Loff is formed. This area is called an offset area, and its width Loff is called an offset length. As is apparent from the figure, the offset length is the same as the width of the sidewall insulator 1106a (sidewall insulator 1106b).

The other parameters used for the calculation are as described above. For the calculation, Synopsys device simulation software, Sentaurus Device was used. FIG. 23 shows the dependence of the drain current (I _d , solid line) and field-effect mobility (μ, dotted line) on the gate voltage (V _g , potential difference between the gate and the source) of the transistor having the structure shown in FIG. Show. The drain current I _d is the drain voltage (a potential difference between the drain and the source) and + 1V, the field effect mobility μ is obtained by calculating the drain voltage is + 0.1 V.

FIG. 23A shows the gate insulating film with a thickness of 15 nm, FIG. 23B shows the thickness of 10 nm, and FIG. 23C shows the thickness of 5 nm. As the gate insulating film becomes thinner, the drain current I _d (off current) particularly in the off state is significantly reduced. On the other hand, there is no conspicuous change in the peak value of the field effect mobility μ and the drain current I _d (on current) in the on state. It was shown that the drain current exceeded 10 μA around the gate voltage of 1V.

FIG. 24 shows the dependency of the drain current I _d (solid line) and the field effect mobility μ (dotted line) on the gate voltage V _g when the offset length Loff is 5 nm for the transistor having the structure shown in FIG. . The drain current I _d is calculated with a drain voltage of +1 V, and the field effect mobility μ is calculated with a drain voltage of +0.1 V. FIG. 24A shows the gate insulating film with a thickness of 15 nm, FIG. 24B shows the thickness of 10 nm, and FIG. 24C shows the thickness of 5 nm.

FIG. 25 shows the gate voltage dependence of the drain current I _d (solid line) and the field effect mobility μ (dotted line) when the offset length Loff is 15 nm for the transistor having the structure shown in FIG. . The drain current I _d is calculated with a drain voltage of +1 V, and the field effect mobility μ is calculated with a drain voltage of +0.1 V. FIG. 25A shows the gate insulating film with a thickness of 15 nm, FIG. 25B shows the thickness of 10 nm, and FIG. 25C shows the thickness of 5 nm.

In either case, the thinner the gate insulating film, the more the off-state current decreases. On the other hand, there is no noticeable change in the peak value of the field-effect mobility μ and the on-state current.

The peak of the field effect mobility μ is about 80 cm ² / Vs in FIG. 23, about 60 cm ² / Vs in FIG. 24 and about 40 cm ² / Vs in FIG. 25, and decreases as the offset length Loff increases. To do. Further, the off-current has a similar tendency. On the other hand, the on-current decreases as the offset length Loff increases, but is much slower than the decrease in off-current. In addition, it was shown that the drain current exceeded 10 μA when the gate voltage was around 1 V.

In this embodiment, electrical characteristics of a transistor in which an oxide semiconductor containing In, Sn, and Zn as main components is used for a semiconductor layer in which a channel is formed will be described.

A transistor in which an oxide semiconductor containing In, Sn, and Zn as main components is used for a semiconductor layer in which a channel is formed can be formed by heating a substrate when forming the oxide semiconductor, or an oxide semiconductor Good characteristics can be obtained by performing heat treatment after the film is formed. Note that the main component refers to an element contained in a composition ratio of 5 atomic% or more.

By intentionally heating the substrate after formation of the oxide semiconductor film containing In, Sn, and Zn as main components, the field-effect mobility of the transistor can be improved. In addition, the threshold voltage of the transistor can be shifted positively to be normally off.

For example, FIGS. 27A to 27C illustrate an oxide semiconductor film having In, Sn, and Zn as main components, a channel length L of 3 μm, and a channel width W of 10 μm, and a gate insulating film having a thickness of 100 nm. It is the characteristic of the used transistor. In addition, _{V d} was set to 10V.

FIG. 27A shows transistor characteristics when an oxide semiconductor film containing In, Sn, and Zn as main components is formed by a sputtering method without intentionally heating the substrate. At this time, the field effect mobility is 18.8 cm ² / Vsec. On the other hand, when the substrate is intentionally heated to form an oxide semiconductor film containing In, Sn, and Zn as main components, field-effect mobility can be improved. FIG. 27B shows transistor characteristics when the substrate is heated to 200 ° C. to form an oxide semiconductor film containing In, Sn, and Zn as main components, and the field-effect mobility is 32.2 cm ² / Vsec. Is obtained.

The field effect mobility can be further increased by performing heat treatment after an oxide semiconductor film containing In, Sn, and Zn as main components is formed. FIG. 27C illustrates transistor characteristics when an oxide semiconductor film containing In, Sn, and Zn as main components is formed by sputtering at 200 ° C. and then heat-treated at 650 ° C. At this time, the field effect mobility is 34.5 cm ² / Vsec.

By intentionally heating the substrate, an effect of reducing water taken in the sputtering film from being taken into the oxide semiconductor film can be expected. Further, by performing heat treatment after film formation, hydrogen, a hydroxyl group, or water can be released from the oxide semiconductor film and removed, and the field-effect mobility can be improved as described above. Such an improvement in field effect mobility is presumed not only to remove impurities by dehydration and dehydrogenation, but also to reduce the interatomic distance by increasing the density. In addition, crystallization can be achieved by removing impurities from the oxide semiconductor to be highly purified. It is estimated that the highly purified non-single-crystal oxide semiconductor can ideally realize field-effect mobility exceeding 100 cm ² / Vsec.

Oxygen ions are implanted into an oxide semiconductor containing In, Sn, and Zn as main components, hydrogen, a hydroxyl group, or water contained in the oxide semiconductor is released by heat treatment, and the oxide semiconductor is formed simultaneously with or after the heat treatment. May be crystallized. Through such crystallization or recrystallization treatment, a non-single-crystal oxide semiconductor with favorable crystallinity can be obtained.

The effect of intentionally heating the substrate to form a film and / or heat-treating after the film formation contributes not only to improving the field-effect mobility but also to making the transistor normally off. . A transistor using an oxide semiconductor film containing In, Sn, and Zn as main components formed without intentionally heating a substrate for a semiconductor layer in which a channel is formed has a negative shift in threshold voltage. Tend. However, when an oxide semiconductor film formed by intentionally heating the substrate is used, this negative shift of the threshold voltage is eliminated. That is, the threshold voltage moves in a direction in which the transistor is normally off, and such a tendency can be confirmed from the comparison between FIG. 27A and FIG.

Note that the threshold voltage can also be controlled by changing the ratio of In, Sn, and Zn. By setting the composition ratio to In: Sn: Zn = 2: 1: 3, the transistor is normally turned off. Can be expected. In addition, when the composition ratio of the target is In: Sn: Zn = 2: 1: 3, an oxide semiconductor film with high crystallinity can be obtained.

The intentional substrate heating temperature or heat treatment temperature is 150 ° C. or higher, preferably 200 ° C. or higher, more preferably 400 ° C. or higher, and the transistor is normally turned off by forming a film at a higher temperature or by heat treatment. Is possible.

In addition, stability against gate bias stress can be improved by intentionally heating the substrate and / or performing heat treatment after the deposition. For example, drifts of less than ± 1.5 V, preferably less than 1.0 V, can be obtained under the conditions of 2 MV / cm, 150 ° C. and 1 hour application, respectively.

Actually, a BT test was performed on the transistor of Sample 1 which was not subjected to heat treatment after the formation of the oxide semiconductor film and Sample 2 which was subjected to heat treatment at 650 ° C.

First, the substrate temperature of 25 ° C., _{V d} of 10V, were measured _V g -I _d characteristics of the transistor. Then, the substrate temperature was set to 0.99 ° C., and _{V d} was set to 0.1 V. V _d represents a drain voltage (a potential difference between the drain and the source). Next, 20 V was applied to V _g so that the electric field strength applied to the gate insulating film was 2 MV / cm, and the voltage was held for 1 hour. Next, _Vg was set to 0V. Next, a substrate temperature of 25 ° C., _{V d} of 10V, were _V g -I _d measurement of the transistor. This is called a plus BT test.

Similarly, a substrate temperature of 25 ° C. First, _{V d} of 10V, were measured _V g -I _d characteristics of the transistor. Then, the substrate temperature was set to 0.99 ° C., and _{V d} was set to 0.1 V. Next, −20 V was applied to V _g so that the electric field strength applied to the gate insulating film was −2 MV / cm, and this was maintained for 1 hour. Next, _Vg was set to 0V. Next, a substrate temperature of 25 ° C., _{V d} of 10V, were _V g -I _d measurement of the transistor. This is called a minus BT test.

The result of the plus BT test of Sample 1 is shown in FIG. 28A, and the result of the minus BT test is shown in FIG. In addition, FIG. 29A shows the result of the plus BT test of Sample 2, and FIG. 29B shows the result of the minus BT test.

The threshold voltage fluctuations of the sample 1 in the plus BT test and the minus BT test were 1.80 V and −0.42 V, respectively. Moreover, the fluctuation | variation of the threshold voltage by the plus BT test of the sample 2 and the minus BT test was 0.79V and 0.76V, respectively.
It can be seen that both Sample 1 and Sample 2 have low threshold voltage fluctuations before and after the BT test and high reliability.

Although heat treatment can be performed in an oxygen atmosphere, first, heat treatment may be performed in an atmosphere containing oxygen after performing heat treatment under nitrogen or an inert gas or under reduced pressure. By first adding oxygen to the oxide semiconductor after dehydration and dehydrogenation, the effect of the heat treatment can be further enhanced. In order to add oxygen later, a method in which oxygen ions are accelerated by an electric field and implanted into the oxide semiconductor film may be applied.

Defects due to oxygen vacancies are likely to be generated at the interface between the oxide semiconductor and the film in contact with the oxide semiconductor, but these defects are regularly generated by excessively containing oxygen in the oxide semiconductor by such heat treatment. This makes it possible to compensate for oxygen deficiency with excess oxygen. Excess oxygen is mainly oxygen present in the lattice. If the oxygen concentration is 1 × 10 ¹⁶ / cm ³ or more and 2 × 10 ²⁰ / cm ³ or less, the oxide semiconductor does not give distortion to the crystal. Can be included.

In addition, a more stable oxide semiconductor film can be obtained by including at least part of crystals in the oxide semiconductor by heat treatment. For example, an oxide semiconductor film formed by sputtering using a target having a composition ratio of In: Sn: Zn = 1: 1: 1 without intentionally heating the substrate is formed by X-ray diffraction (XRD: X-Ray Diffraction). ) A halo pattern is observed. The formed oxide semiconductor film can be crystallized by heat treatment. Although the heat treatment temperature is arbitrary, for example, by performing heat treatment at 650 ° C., a clear diffraction peak can be observed by X-ray diffraction.

Actually, an XRD analysis of an In—Sn—Zn-based oxide was performed. For XRD analysis, an X-ray diffractometer D8 ADVANCE manufactured by Bruker AXS was used, and measurement was performed by the Out-of-Plane method.

Samples A and B were prepared as samples subjected to XRD analysis. A method for manufacturing Sample A and Sample B will be described below.

An In—Sn—Zn-based oxide film was formed to a thickness of 100 nm over a dehydrogenated quartz substrate.

The In—Sn—Zn-based oxide was formed using a sputtering apparatus with an electric power of 100 W (DC) in an oxygen atmosphere. As a target, an In—Sn—Zn—O target of In: Sn: Zn = 1: 1: 1 [atomic ratio] was used. The substrate heating temperature at the time of film formation was 200 ° C. The sample thus prepared was designated as Sample A.

Next, heat treatment was performed at a temperature of 650 ° C. on the sample manufactured by the same method as Sample A. In the heat treatment, first, heat treatment is performed for 1 hour in a nitrogen atmosphere, and heat treatment is further performed for 1 hour in an oxygen atmosphere without lowering the temperature. The sample thus prepared was designated as Sample B.

FIG. 30 shows XRD spectra of Sample A and Sample B. In sample A, no crystal-derived peak was observed, but in sample B, 2θ was observed in the vicinity of 35 deg and from 37 deg to 38 deg.

In this manner, the characteristics of a transistor can be improved by intentionally heating an oxide semiconductor containing In, Sn, and Zn as main components and / or performing heat treatment after the film formation.

This substrate heating or heat treatment has an action of preventing or removing hydrogen and hydroxyl groups, which are malignant impurities for the oxide semiconductor, from the film. In other words, high purity can be achieved by removing hydrogen which is a donor impurity in an oxide semiconductor, whereby the transistor can be normally turned off and the oxide semiconductor can be highly purified. As a result, the off-current can be reduced to 1 aA / μm or less. Here, the unit of the off current value represents a current value per channel width of 1 μm.

FIG. 31 shows the relationship between the off-state current of a transistor and the inverse of substrate temperature (absolute temperature) at the time of measurement. Here, for simplicity, the horizontal axis represents a numerical value (1000 / T) obtained by multiplying the reciprocal of the substrate temperature at the time of measurement by 1000.

Specifically, as shown in FIG. 31, when the substrate temperature is 125 ° C., 0.1 aA / μm (1 × 10 ⁻¹⁹ A / μm) or less, and when it is 85 ° C., 10 zA / μm (1 × 10 ⁻²⁰ A / μm) or less. Since the logarithm of the current value is proportional to the reciprocal of the temperature, it is expected to be 0.1 zA / μm (1 × 10 ⁻²² A / μm) or less at room temperature (27 ° C.). Therefore, the off-current is 1 aA / μm (1 × 10 ⁻¹⁸ A / μm) or less at 125 ° C., 100 zA / μm (1 × 10 ⁻¹⁹ A / μm) or less at 85 ° C., and 1 zA / μm (1 × 10 ⁻²¹ A / μm) or less. It is clear that these off-current values are extremely low compared to a transistor using Si as a semiconductor film.

However, in order to prevent hydrogen and water from entering the oxide semiconductor film during film formation, leakage from the outside of the film formation chamber and outgassing from the inner wall of the film formation chamber are sufficiently suppressed to increase the purity of the sputtering gas. It is preferable to plan. For example, the sputtering gas is preferably a gas having a dew point of −70 ° C. or lower so that water is not included in the film. In addition, it is preferable to use a highly purified target so that the target itself does not contain impurities such as hydrogen and water. An oxide semiconductor containing In, Sn, and Zn as main components can remove water in the film by heat treatment, but has a higher water discharge temperature than an oxide semiconductor containing In, Ga, and Zn as main components. Therefore, it is preferable to form a film not containing water from the beginning.

In addition, the relationship between the substrate temperature and the electrical characteristics of the transistor using Sample B that was heat-treated at 650 ° C. after the oxide semiconductor film was formed was evaluated.

The transistor used for the measurement has a channel length L of 3 μm, a channel width W of 10 μm, Lov of 0 μm, and dW of 0 μm. In addition, _{V d} was set to 10V. The substrate temperatures were -40 ° C, -25 ° C, 25 ° C, 75 ° C, 125 ° C and 150 ° C. Here, in the transistor, the overlapping width between the gate electrode and the pair of electrodes is referred to as Lov, and the protrusion of the pair of electrodes with respect to the oxide semiconductor film is referred to as dW.

FIG. 32 shows the dependence of I _d (solid line) and field-effect mobility (dotted line) on V _g . FIG. 33A shows the relationship between the substrate temperature and threshold voltage, and FIG. 33B shows the relationship between the substrate temperature and field effect mobility.

FIG. 33A shows that the threshold voltage decreases as the substrate temperature increases. In addition, the range was 1.09V--0.23V at -40 degreeC-150 degreeC.

FIG. 33B shows that the field effect mobility decreases as the substrate temperature increases. Incidentally, the range was 36cm ² / Vs~32cm ² / Vs at -40 ° C. to 150 DEG ° C.. Therefore, it can be seen that the variation in electrical characteristics is small in the above temperature range.

According to the transistor using an oxide semiconductor whose main component is In, Sn, and Zn in the semiconductor layer in which the channel is formed as described above, the field-effect mobility is 30 cm ² while maintaining the off-current at 1 aA / μm or less. / Vsec or more, preferably 40 cm ² / Vsec or more, more preferably 60 cm ² / Vsec or more, and can satisfy the on-current value required for LSI. For example, in an FET with L / W = 33 nm / 40 nm, an on-current of 12 μA or more can flow when the gate voltage is 2.7 V and the drain voltage is 1.0 V. In addition, sufficient electrical characteristics can be ensured even in a temperature range required for the operation of the transistor. With such characteristics, an integrated circuit having a new function can be realized without sacrificing operation speed even if a transistor formed of an oxide semiconductor is mixedly mounted in an integrated circuit formed of a Si semiconductor. be able to.

100 Divider circuit 101 DFF circuit 102 DFF circuit 103 DFF circuit 111 Terminal unit 112 Node 113 Node 114 Terminal unit 115 Node 116 Node 121 Inverter 122 Inverter 123 Inverter 124 Analog switch 125 Analog switch 126 Clocked inverter 127 Clocked inverter 131 P-type Transistor 132 n-type transistor 133 n-type transistor 134 p-type transistor 135 p-type transistor 136 n-type transistor 200 Divider circuit 201 FF circuit 202 FF circuit 203 FF circuit 211 Terminal portion 212 Node 213 Node 214 Terminal portion 215 Node 216 Node 217 Node 218 Node 219 Node 220 Node 221 Inverter 222 Inverter 223 Node 231 Transistor 232 Transistor 233 Transistor 234 Transistor 235 Transistor 236 Transistor 237 Transistor 238 Transistor 251 FF circuit 252 Capacitor 253 Capacitor 261 FF circuit 300 Frequency divider 301 FF circuit 302 FF circuit 303 FF circuit 311 Terminal unit 312 Node 313 Node 314 Terminal unit 315 Node 316 Node 341 Inverter 700 Substrate 701 Insulating film 702 Semiconductor film 703 Gate insulating film 704 Impurity region 705 Mask 706 Opening 707 Gate electrode 708 Conductive film 709 Impurity region 710 Channel formation region 711 Impurity region 712 Insulating film 713 Insulating film 716 Oxide Physical semiconductor layer 719 conductive film 720 conductive film 721 gate insulating film 722 gate electrode 724 insulating film 725 opening 26 wiring 727 insulating film 731 transistor 732 transistor 901 transistor 902 base film 903 oxide semiconductor layer 904 source electrode 905 drain electrode 906 gate insulating film 907 gate electrode 908 high-concentration region 909 channel formation region 910 protective insulating film 911 transistor 912 base film 913 Oxide semiconductor layer 914 Source electrode 915 Drain electrode 916 Gate insulating film 917 Gate electrode 918 High concentration region 919 Channel formation region 920 Protective insulating film 921 Transistor 922 Base film 923 Oxide semiconductor layer 924 Source electrode 925 Drain electrode 926 Gate insulating film 927 Gate electrode 928 High concentration region 929 Low concentration region 930 Side wall 931 Channel formation region 932 Protective insulating film 941 Transistor 942 Base film 9 3 Oxide semiconductor layer 944 Source electrode 945 Drain electrode 946 Gate insulating film 947 Gate electrode 948 High concentration region 949 Low concentration region 950 Side wall 951 Channel formation region 952 Protective insulating film 961 Transistor 962 Base film 963 Oxide semiconductor layer 964 Source electrode 965 Drain electrode 966 Gate insulating film 967 Gate electrode 968 High concentration region 969 Low concentration region 970 Side wall 971 Channel formation region 972 Protective insulating film 973 Insulating film 974 Electrode 975 Electrode 1101 Base insulating layer 1102 Insulator 1104 Gate insulating film 1105 Gate 1107 Insulator 7001 Case 7002 Display portion 7011 Case 7012 Display portion 7013 Support base 7021 Case 7022 Display portion 7031 Case 7032 Case 7033 Display portion 7034 Display portion 7035 Microphone 7036 Speaker 7037 Operation key 7038 Stylus 7041 Case 7042 Display unit 7043 Audio input unit 7044 Audio output unit 7045 Operation key 7046 Light receiving unit 7051 Case 7052 Display unit 7053 Operation key 9900 Substrate 9901 ALU
9906 Register
9909 ROM
1103a Semiconductor region 1103b Semiconductor region 1103c Semiconductor region 1106a Side wall insulator 1106b Side wall insulator 1108a Source 1108b Drain

Claims (8)

Having a first inverter and a second inverter;
a first transistor and a fifth transistor which are p-type transistors;
second to fourth transistors and sixth to eighth transistors, which are n-type transistors,
One of the source and the drain of the first transistor is electrically connected to one of the source and the drain of the fifth transistor and a first power source,
The other of the source and the drain of the first transistor is electrically connected to one of the source and the drain of the second transistor;
The other of the source and the drain of the second transistor is electrically connected to one of the source and the drain of the third transistor;
The other of the source and the drain of the fifth transistor is electrically connected to one of the source and the drain of the sixth transistor;
The other of the source and the drain of the sixth transistor is electrically connected to one of the source and the drain of the seventh transistor;
The other of the source and the drain of the third transistor is electrically connected to the other of the source and the drain of the seventh transistor and a second power source;
A gate of the first transistor is electrically connected to a gate of the second transistor, a gate of the eighth transistor, and an input of the first inverter;
One of a source and a drain of the eighth transistor is electrically connected to the other of the source and the drain of the first transistor;
The other of the source and the drain of the eighth transistor is electrically connected to the gate of the seventh transistor;
An input of the second inverter is electrically connected to the other of the source and the drain of the fifth transistor;
An output of the second inverter is electrically connected to one of a source and a drain of the fourth transistor;
The other of the source and the drain of the fourth transistor is electrically connected to the gate of the third transistor;
The output of the first inverter is electrically connected to the gate of the fourth transistor, the gate of the fifth transistor, and the gate of the sixth transistor ,
The input terminal is electrically connected to the input of the first inverter,
An output terminal is electrically connected to an input of the second inverter . In claim 1,
The frequency dividing circuit, wherein the first power supply supplies a higher potential than the second power supply. In claim 1 or claim 2,
A frequency dividing circuit, wherein a capacitor is electrically connected to at least one of a source and a drain of the eighth transistor or an input of the second inverter. In any one of Claims 1 thru | or 3,
In the frequency divider circuit, the semiconductor layer in which the channel is formed is an oxide semiconductor. In any one of Claims 1 thru | or 4,
In the eighth transistor, the semiconductor layer in which a channel is formed is an oxide semiconductor. In any one of Claims 1 thru | or 5,
In at least one of the second transistor and the third transistor, a semiconductor layer in which a channel is formed is an oxide semiconductor. In any one of Claims 1 thru | or 6,
In at least one of the sixth transistor and the seventh transistor, a semiconductor layer in which a channel is formed is an oxide semiconductor. In any one of Claims 1 thru | or 7,
A semiconductor device using the frequency divider circuit.